Previous Seminars

Title:  Strange Vortices in Spinor Superfluids

David Hall, Amherst University

Tuesday, January 24th, 2023

2:30-3:30pm, 105 Lin Hall

Abstract:  Vortices play fundamental roles in science, mathematics, and technology. Many aspects of vortices in superfluids, such as the quantization of circulation, have been extensively studied. With the addition of a spin degree of freedom, however, less-familiar phenomena are encountered:  spinor vortices can have no core with circulation that is not quantized, or they can be singular with fractional units of circulation, depending on the underlying magnetic phase of the superfluid they inhabit. Singular spinor vortices can also have unusual vortex cores that consist of superfluid in magnetic phases distinct from the vortex itself. In this talk I will describe our recent experiments with spinor vortices in dilute-gas Bose-Einstein condensates, as well as experimental progress towards realizing "noncommuting" vortices in magnetic phases with only discrete symmetries. These strange vortices can leave behind traces of their collisions in the form of "rung vortices," with possible implications for interferometry and quantum information.

Title:  Metal-dielectric photonic crystal organic light emitting diodes.

Matthew White, University of Vermont

Tuesday, January 31st, 2023

2:30-3:30pm, 105 Lin Hall

Abstract:  A microcavity OLED, consisting of a conventional OLED stack with two metallic mirror electrodes, shows narrow-band emission centered around specific peak resonant wavelengths. These cavity modes are analogous to the energy states found in any resonator system, including musical instrument strings and 1-dimensional quantum square wells. We demonstrate how the microcavity OLED can be used as a unit cell in a planar, 1-dimensional photonic crystal and explore how the dimensional and material properties of the device impact the spectral electroluminescence dispersion. Stacking N microcavities splits the resonant modes into N discrete states; a photonic band centered at the single microcavity state. Devices are fabricated by thermal evaporation with in-vacuo shadow mask transfers to enable parallel-connected unit cells. The photonic density of states is controlled by varying the thickness of the semitransparent metal mirror electrodes. A Peierls bandgap is tuned by varying only alternate mirror thicknesses. Device parameters, including N, the thickness of the semi-transparent metal electrodes, and dipole emission position are correlated to emission properties such as peak wavelength, FWHM, and Q-factor for each of the photonic states. The band structure is optimized by employing optically similar silver alloys as anode and cathode. The experimental results are guided by a predictive computationalmodeling tool, which is critically important for the complex-architecture devices.

Title:  Dynamics of Bose-Einstein condensates in a moving optical lattice

Qingze Guan, Washington State University

Friday, February 10th, 2023

2:30-3:30pm, 105 Lin Hall

Abstract:  Ultracold quantum gases are powerful platforms for building quantum simulators due to the long coherence time and the high tunability. By manipulating laser-atom interactions, various quantum systems can be simulated in cold atoms, such as Bloch oscillation of electrons in solids, Josephson junction oscillations in superconductors, matter with synthetic gauge fields, and topological materials. This presentation will focus on the dynamics of Bose-Einstein condensates in a moving optical lattice with particular emphasis placed on the role of interaction in the system. It will cover the Ramsey interferometers, self-trapping, Landau-Zener tunneling, spin dynamics, and scattering phenomena. The good agreement between theory and experiment validates such a system as a testbed for theories and a powerful platform for other quantum simulations.

Title:  Quantum Back-action Limits in Dispersively Measured Bose-Einstein Condensates

Emine Altuntas, JQI,  University of Maryland

Friday, February 17th,

2:30-3:30pm, 105 Lin Hall

Abstract:  Most quantum technologies simultaneously require quantum limited measurements and feedback control to establish and maintain quantum coherence and entanglement, with applications ranging from quantum state preparation to quantum error correction. Large-scale applications of these capabilities hinge on understanding system-reservoir dynamics of many-body quantum systems, whose Hilbert space grows exponentially with system size. Ultracold atoms are an ideal platform for understanding the system-reservoir dynamics of many-body systems. In this talk, I will present the characterization of measurement back-action in atomic Bose-Einstein condensates, weakly interacting with a far-from resonant, i.e., dispersively interacting, laser beam. We theoretically describe this process using a quantum trajectories approach where the environment measures the scattered light and I will present our measurement model based on an ideal photodetection mechanism. Next, I will discuss our experimental quantification of the resulting wavefunction change with two observations: the contrast of a Ramsey interferometer [1] and the deposited energy [2]. These results are necessary precursors for achieving true quantum back-action limited measurements of quantum gases and open the door to quantum feedback control of ultracold atoms.

[1] E. Altuntaş and I. B. Spielman, arXiv preprint arXiv:2209.04400 (2022).

[2] E. Altuntaş and I. B. Spielman, arXiv preprint arXiv:2212.03431 (2022).

Title: Quantum Computing with Neutral Atoms.

Ivan Deutsch, University of New Mexio

Friday, February 24th, 2023

2:30-3:30pm, 105 Lin Hall

Abstract:  One of the earliest proposals for scalable quantum computers was to encode qubits in individual optically- trapped, ultracold neutral atoms.  Like their more famous cousins, atomic ions, qubits encoded in the energy levels of neutral atoms are all identical, can have long coherence times, and can be controlled with a variety of magneto-optical fields, with tools that build on decades of development for atomic clocks and precision metrology. Unlike with ions, quantum computing architectures have proceeded more slowly, as neutral atoms are harder to trap and they only weakly interact in their ground state.  New developments in trapping and laser technology has now opened the door to high-fidelity operation with potentially hundreds to thousands of qubits - neutral atoms are back in the game!  In this seminar I will discuss how high-fidelity quantum logic can be implemented through coherent control of superpositions of atoms in ground and highly excited Rydberg states.  I will also describe how optimal control can be used to implement a variety of protocols for quantum information processing with neutral atoms, including the performing quantum logic with “qudecimals" (d=10 dimensional systems) encoded in nuclear spins.  

Title:  Coherent photoexcited dynamics in molecular systems

Sergei Tretiak, Los Alamos National Lab

Friday, March 3rd, 2023

2:30-3:30pm, 105 Lin Hall

Abstract:  I will overview some applications of  Non-adiabatic EXcited-state Molecular Dynamics (NEXMD) framework developed at several institutions and is released to public. The NEXMD code is able to simulate tens of picoseconds photoinduced dynamics in large molecular systems and dense manifold of interacting and crossing excited states. As an application, I will exemplify ultrafast coherent excitonic dynamics guided by intermolecular conical intersections (CoIns). Both simulations and time-resolved two-dimensional electronic spectroscopy track the coherent motion of a vibronic wave packet passing through CoIns within 40 fs, a process that governs the ultrafast energy transfer dynamics in molecular aggregates. Our results suggest that intermolecular CoIns may effectively steer energy pathways in functional nanostructures.  In the second example, we use dynamical simulations to compute X-ray Raman signals, which are able to monitor the coherence evolution. The observed coherences have vibronic nature that may survives multiple conical intersection passages for several hundred femtoseconds at room temperature. These spectroscopic signals are possible to measure at XFEL facilities, paving the way for detailed coherence measurements in functional organic materials. Observed relationships between spatial extent/properties of electronic wavefunctions and resulting electronic functionalities allow us to understand and potentially manipulate excited state dynamics and energy transfer pathways toward optoelectronic applications.

Relevant references

1. A. De Sio, E. Sommer, X. T. Nguyen, L. Gross, D. Popović, B. Nebgen, S. Fernandez-Alberti, S. Pittalis, C. A. Rozzi, E. Molinari, E. Mena-Osteritz, P. Bäuerle, T. Frauenheim, S. Tretiak, C. Lienau, “Intermolecular conical intersections in molecular aggregates” Nature Nanotech. 16, 63 – 68 (2021). 
2. D. Keefer, V. M. Freixas, H. Song, S. Tretiak, S. Fernandez-Alberti, and S. Mukamel, “Monitoring Molecular Vibronic Coherences in a Bichromophoric Molecule by Ultrafast X–Ray Spectroscopy” Chem. Sci. 12, 5286 – 5294 (2021).  
3. V. M. Freixas, D. Keefer, S. Tretiak, S. Fernandez-Alberti, and S. Mukamel, “Ultrafast coherent photoexcited dynamics in a trimeric dendrimer probed by X-ray stimulated-Raman signals,” Chem. Sci., 13, 6373 – 6384 (2022).

Title: Atomic clocks and quantum sensors for advancing science in microgravity and space environment

Nan Yu,  NASA Jet Propulsion Laboratory

Tuesday, March 7th, 2023
2:30-3:30pm, Lin Hall 

Abstract: With the advent of laser cooling, trapping, and manipulation of atomic particles, advanced atomic clocks, atom interferometer sensors, and atomic quantum systems have been demonstrated in research laboratories. These new technologies and resulting capabilities will have a significant and diverse impact on space science and exploration, including gravity measurements for earth and planetary sciences, gravitational wave detection, direct detection of dark energy and matter in astrophysics and tests of fundamental physics. This talk will provide an overview of clock and quantum sensor technologies and their applications in space with a focused discussion on the direct detection of dark energy scalar field experiment on Einstein Elevator.

Title: Improving the Efficiency and Safety of Battery and Fuel Cell Materials through Computational Analysis

Michelle Johannes,  NRL

Tuesday, March 21st, 2023
2:30-3:30pm, Lin Hall 

Abstract: Although batteries and fuel cells work as complete and complex electrochemical systems, but a surprising number of their performance metrics can be traced back to the individual materials components that comprise the anode, cathode and electrode.   Optimizing these materials in terms of cost, efficiency and safety is a concern for the commercial and government sectors.

In this talk, I will discuss how costly laboratory searches can often be replaced by “cheap” computational simulations and how the underlying materials physics, including subtle quantum mechanical effects, can determine battery/fuel cell performance.   I will briefly introduce density functional theory (DFT), a fully quantum mechanical description of how electrons organize, reorganize and move in relevant materials  and then describe some successes (and failures) of the method in designing and improving common battery materials.   I will highlight the property of “transport” - both ionic and electronic which is often the determining factor in whether a material is useful or not for electrochemical systems.  

Title: Quantum state control of single molecular ions for quantum information processing and precision spectroscopy

Chin-Wen Chou,  NIST-Boulder

Tuesday, March 28th, 2023
2:30-3:30pm, Lin Hall 

Abstract: Over the past decades, atoms are trapped and laser cooled to near zero temperature, minimizing the motional effects in spectroscopy. Internal states of atoms can be coherently manipulated and prepared in pure quantum states, including entangled states that are impactful in quantum information processing, sensing, and metrology. This talk will describe the effort of the Ion Storage group at NIST in bringing molecular ions to equal footings with atoms in terms of state control and spectroscopic precision. The project builds on laser cooling and trapping techniques, frequency comb technology, and quantum-logic spectroscopy protocols nowadays routinely employed in cold-atom research and trapped ion optical clocks. That enables demonstrations, on single molecular ions, of coherent quantum state manipulation, nondestructive state detection, spectroscopy with better than part-per-trillion resolution, and quantum entanglement. The group is exploring new opportunities in physics and chemistry offered by the richer structure and broader species selections in molecules.

Title:  Controlling spin and light at room temperature in Lead-Halide Inspired Hybrid Semiconductors

Matthew Beard, NREL

Friday, April 7th, 2023

2:30-3:30pm, 105 Lin Hall

Abstract:  In this presentation I will discuss our studies of controlling the charge carrier dynamics, light/matter interactions, and spin populations in metal-halide organic/inorganic hybrid systems. 

Lower dimensional perovskites are of particular interest since the lower degree of symmetry of the metal-halide connected octahedra and the large spin-orbit coupling can potentially lift the spin degeneracy. To achieve their full application potential, an understanding of spin-relaxation in these systems are needed. Here, we report an intriguing spin-selective excitation of excitons in a series of 2D lead iodide perovskite (n = 1) single crystals by using time- and polarization-resolved transient reflection spectroscopy. Exciton spin relaxation times as long as ~26 ps at low excitation densities and at room temperature were achieved for a system with small binding energy, 2D EOA₂PbI₄(EOA=ethanolamine).

We have recently studied and developed a novel class of chiral hybrid semiconductors based upon layered metal-halide perovskite 2D Ruddlesden-Popper type structures.  These systems exhibit chiral induced spin selectivity (CISS) whereby only one spin sense can transport across the chiral layer and the other spin sense is blocked for one handedness of the chiral perovskite layer.  We show that chiral perovskite layers are able to achieve > 80% spin-current polarization.  We have also studied spin-injection from the chiral-layer to a non-chiral perovskite layer and find high spin-injection efficiency. We developed novel spin-based LEDs using non-chiral perovskite NCs as the light emitting layer that promotes light emission at a highly spin-polarized interface.  The LED spin-polarization is limited by spin-depolarization within the MHP NCs. 

Finally, if time permits I will discuss our efforts for developing novel organic inorganic magnetic systems.  Low dimensional copper halide perovskite anitferromagnets display interesting a tunable magnonic behavior.  The organic cations offer interesting opporutnies to control the weak intralayer AFM interaction as well as symmetry breaking in the inorganic layer.   

Title:  Integrated Optical Control of Atomic Quantum Systems

Amit Agrawal, NIST

Friday, April 7th, 2023

2:30-3:30pm, 105 Lin Hall

Abstract:  Over the last decade, flat optical elements composed of an array of deep-subwavelength dielectric or metallic nanostructures of nanoscale thicknesses – referred to as metasurfaces – have revolutionized the field of optics. Because of their ability to impart an arbitrary phase, polarization or amplitude modulation to an optical wavefront as well as perform multiple optical transformations simultaneously on the incoming light, they promise to replace traditional bulk optics in applications requiring compactness, integration and/or multiplexing. Recent demonstrations including imaging, polarimetry, quantum-light generation and LIDAR demonstrate the range of technologies where metasurfaces have already had a significant impact. In this talk, we demonstrate the versatility of wavefront shaping metasurfaces as a compact, efficient and multifunctional interface to trap neutral atoms or address trapped ions for applications in quantum information science and atomic clocks. In another integration step, combining metasurfaces with photonic integrated circuits, replacing bulk optical elements, promises increased complexity and functionality in a batch-fabricated optical microsystem ultimately fully replacing the laboratory optical table to enable cold atom clocks and quantum computers.

Title:  Exciton fine structure in perovskite nanocrystal quantum dots

Peter Sercel, California Institute of Technology

Friday, April 28th, 2023

2:30-3:30pm, 105 Lin Hall

Abstract:  Colloidal lead halide perovskite nanocrystal quantum dots are promising as classical light sources for devices such as light emitting diodes and displays owing to the fast, efficient   radiative decay in these materials.  They are currently being considered for potential applications in quantum information processing as well since, for example, they can emit single photons or correlated photon pairs, and have been shown to have long optical coherence times.  Such applications hinge to an extent on our understanding and control of the exciton fine structure.

In this talk we will discuss the exciton fine structure in perovskite nanocrystals and its determinants: The electron-hole exchange interaction, which splits the exciton into a dark (optically inactive) singlet level and a bright (optically active) triplet, the effect of the crystal lattice symmetry in splitting the bright triplet, and the possible role of the Rashba effect.  We will focus then on the particular role of the nanocrystal shape in conjunction with the “long range” exchange interaction in controlling the fine structure.

 A unique aspect of the structure of perovskite nanocrystals is a roughly 45 degree misalignment between the orthorhombic crystal lattice vectors from the nanocrystal bounding facets.  This misalignment breaks the orthorhombic symmetry, creating coupling between bright exciton states. The result is a previously unrecognized avoided-crossing “fine-structure gap” within the bright triplet which can be observed via quantum beating in ensemble-level transient absorption measurements [1].    We predict as a further consequence the existence of chiro-optical effects, which are a manifestation of “extrinsic chirality”. 

[1] Y.  Han, W. Liang, Y. Li, X. Lin, F. Sun, F. Zhang, P.C. Sercel, K. Wu, Lattice distortion inducing exciton splitting and coherent quantum beating in CsPbI₃ perovskite quantum dots, Nature Materials, 21, 1282–1289, (2022.)

Title: Liquid and solid like behavior of ultra-dilute Bose-Einstein condensates of magnetic atoms

P. Blair Blakie, Department of Physics, University of Otago, Dunedin, New Zealand 

Monday, May 15th, 2023
2:30-3:30pm, 105 Lin Hall 

Abstract: Over the last decade, ultra-cold gases of highly magnetic lanthanide atoms have emerged as an intriguing platform for studying superfluid gases with long-range interactions.

One surprising discovery in these systems was the observation that beyond meanfield effects, arising from quantum fluctuations, could become important in the behavior of the gas. This has led to liquid like behavior, such as the production of quantum droplets, and more recently, a crystallization transition to a supersolid state of matter. These curious phenomena occur in an ultra-dilute gas about a billion times less dense than ordinary water! 

I will overview some of the basic theory of this system and discuss some of the wonderful progress made in experiments studying Bose-Einstein condensates of highly magnetic atoms.

Title: High-entropy oxides as candidates for artificial magnetoelectrics

Robert Kruk,  Karlsruhe Institute of Technology

Tuesday, May 23rd, 2023
2:30-3:30pm, Lin Hall 

Abstract: The quest for artificial, heterostructured magnetoelectrics is driving the search for new magnetic materials that exhibit enhanced sensitivity to voltage stimulation. In principle, the system of choice for this purpose can be the new class of materials known as High Entropy Oxides (HEOs). HEOs are single phase solid solutions consisting of five or more elements in equiatomic or near-equiatomic proportions incorporated into the cationic sub-lattice(s). What sets HEOs apart is their remarkable chemical complexity, encapsulated within a single crystallographic structure, often resulting in unique functionalities. From a local structure standpoint, HEOs exhibit an exceptionally large number of distinct metal-oxygen-metal pairings. Consequently, the magnetic correlations in HEOs, influenced by the coordination geometry, valence, spin state, and type of hybridized metal cations, are naturally influenced by an extensive variety of neighboring ionic configurations. These conditions give rise to a complex magneto-electronic free-energy landscape within HEOs, potentially leading to the stabilization of unconventional spin-electronic states. This form of inherently imbalanced magnetism has the potential to be influenced by external stimuli, such as voltage, presenting opportunities for the development of artificial magnetoelectrics. Examples of these systems, including perovskites and spinels, will be discussed in the context of their magneto-electronic properties, which are a consequence of the extreme local chemical disorder.

Title:  New Materials Discovery by Molecular-beam Epitaxy 

Hanjong Paik, OU  

Tuesday, August 23,  2022
2:30-3:30pm (105 Lin Hall/Zoom Link will be announced).

Abstract:   The synthesis of complex oxide thin films by the molecular-beam epitaxy (MBE) technique provides a great potential for unleashing novel and hidden properties of the material from the dull ground states. Especially, when it utilizes the lattice coherency from the substrates, i.e., strain, the properties of thin films can be dramatically altered in comparison to their bulk form. Occasionally, this approach results in metastable phase and pseudomorphic polymorphism, thus, introducing the unexpected emergent properties owing to the power of epitaxial-strain-symmetry-stabilization at the interface. Therefore, the thin-film approach for new quantum material discovery will be the ultimate platform for the fundamental study of new quantum phenomena at the surface and interface. 

  In this talk, I would like to present how ozone-assist oxide MBE can be useful to discover new material properties, especially, relevant to the strongly correlated electronic system. I will talk about (1) room temperature high-electron-mobility and its 2DEG behavior of the perovskite stannate interface for the transparent power electronics (2) how simple metal ruthenium dioxide becomes a superconductor via. strain-stabilization, and (3) realization of epitaxial topological crystalline insulator Sr₃SnO anti-perovskite system with in-situ spectroscopy. In addition to describing the above material synthesis and characterization, I also would like to discuss several challenging materials systems, for example, some cubic-to-hexagonal perovskite polymorphic systems, noble pyrochlore oxides system, and materials growth challenges containing alkaline metal elements (i.e., Li-, K-, Na- containing material system) for the fundamental study of quantum materials. 

Title:    Developing Quantum Information Devices and Systems using New Materials, Experiments, Nanostructures and Data-driven Models

Safura Sharifi, OU Dept. of Electrical and Computer Engineering

Tuesday, September 6, 2022
2:30-3:30pm (105 Lin Hall).

Abstract:   Quantum devices and systems are the heart of revolutionary technologies that open up new ways to collect and process information, perfectly secure communications, optimize computation problems, accurately measure physical phenomena, and many more. My research includes the applications of new materials, experiments, nanostructures, and data-driven models to impact the field of quantum science and technology. My presentation will explain integrating computational and experimental techniques to introduce new development, design, and implementation tools for quantum devices and quantum optical systems with more diverse and enhanced functionalities. My research presentation will discuss combining the knowledge of designing the optical structures and the dominant performance of rare-earth material to generate, manipulate, and store quantum light as well as control and use coherent atom-atom interactions for quantum information processing. In addition, I will discuss how to engineer the functionality of multilayer nanostructures to control optical properties for various applications ranging from spacecraft thermal control systems to advanced gravitational wave detectors that can minimize thermal noise below the standard quantum limit. Furthermore, I will provide my perspective on developing predictive performance models using computational and machine learning techniques to combat noise in optical and quantum optical systems and predict the performance of future experiments.

Title:  Colloidal Assembly at Fluid Interfaces

Sepideh Razavi, OU Dept. of Chemical, Biological and Medical Engineering.

Friday, September 16, 2021
2:30-3:30pm,  105 Lin Hall

Abstract:  The ubiquity of self-assembly - the process of creating organizational order in systems of components - in nature has inspired technological developments towards synthetic building blocks that assemble into desirable structures with a unique set of properties. Isotropic spherical colloids are a simple example of such building blocks where their spatial arrangement yields photonic crystals that exhibit structural color. The key step towards engineering the assembly process is the ability to tune the interparticle interactions. There is a concerted effort in the field to identify the factors that impact the interparticle interactions and control the assembly process. How is the assembly in bulk different from the 2D assembly in the presence of a fluid interface? What happens when shape or surface anisotropic (i.e., Janus) particles are used as building blocks for assembly? In this talk, I will present experiments on the application of fluid interfaces as a template for assembly; specifically, I will discuss the role of particle surface properties in tuning the mechanical stability and flow behavior of the assembled monolayer, important for applications in which the interface undergoes large deformations producing compression and shear stresses at the interface.

Title:  Molecular transistors as substitutes for quantum information applications

Mario Borunda, Oklahoma State University

Friday, September 23, 2022
2:30-3:30pm,  105 Lin Hall

Abstract:  Applications of quantum information generally rely on the generation and manipulation of qubits. Still, there are ways to envision a device with a continuous readout but without the entangled states. In this talk, I will discuss an alternative to the qubit, namely the solid-state version of the Mach–Zehnder interferometer, in which the local moments and spin polarization replace light polarization. Transistors based on such systems lead to the possibility of fabricating logic gates that do not require entangled states.

Title:    Strong coupling theory of twisted multilayer graphene systems: correlatedinsulators, collective excitations and superconductivity   

Eslam Khalaf, Harvard University

Tuesday, October 4th, 2022

2:30-3:30pm (105 Lin Hall/Zoom Link will be announced).

Abstract:    I will discuss a recently developed strong coupling theory of magic-angle twisted bilayer graphene. I will begin by showing how the electronic structure of twisted bilayer graphene makes it possible to relate its flat bands to the lowest Landau levels. This leads to a model of twisted bilayer graphene consisting of two sets of U(4) symmetric Landau-level-like Chern bands with opposite Chern numbers that are tunnel-coupled. I will show how this model broadly captures most of the observed features of twisted bilayer graphene: correlated trivial and topological Chern insulators at integer fillings, fractional Chern insulators and superconductivity. The correlated insulators are understood as generalized quantum Hall ferromagnets. I will then discuss the nature of charged excitations on top of such correlated insulators showing that they admit non-trivial charged excitations in addition to single-particle excitations. These excitations are intimately tied to band topology and can take the form of skyrmions -- real space spin textues -- or spin polarons -- bound states of an electron and a spin waves. I will show that there is a very natural mechanism for superconductivity which leads to pairing of these charged excitations. This mechanism is purely repulsive in origin and relies on band topology in a fundamental way. At the end, I will discuss how these insights generalize to a class of multilayer graphene systems with alternating twist angle and contrast the properties of these systems compared to their bilayer counterpart.

Title:    CANCELLED - Will be rescheduled

Alexander Efros, Naval Research Lab

Tuesday, October 18th, 2022
2:00-3:00pm (105 Lin Hall/Zoom Link will be announced).

Abstract:   

Title:    Entanglement and learnability transitions

Sarang Gopalakrishnan, Princeton University

Tuesday, October 25th, 2022
2:30-3:30pm (105 Lin Hall/Zoom Link will be announced).

Abstract:    Continuously monitored quantum systems can undergo "entanglement transitions" in their steady states (conditioned on the measurement outcomes). I will briefly review our understanding of entanglement transitions and why it is challenging to observe them in realistic experiments. I will introduce a variant on the entanglement transition, called the "charge sharpening" transition, and explain how it can be related to a transition in the ability of an eavesdropper to "learn" the state of a system using local measurements.

Title:  Quantum Simulation and Quantum State Engineering: Prospects and Challenges

 Vito Scarola, Virginia Tech.

Friday, November 4th, 2022
2:30-3:30pm,  105 Lin Hall

Abstract:  Analogue and digital quantum simulation might offer solutions to important but otherwise intractable models.  Yet challenges, such as heating in analogue simulators and noise in digital quantum devices, remain as obstacles.  My theory group seeks to guide experimental setups and construct methods for implementing quantum simulation.  I will review our theory work and experimental progress in using atoms in optical lattices as analogue simulators to probe the phase diagram of the Fermi-Hubbard model.  I will also discuss digital quantum simulation in near term devices.  Here noise limits coherence and therefore gate depth.  I will discuss new ideas for constructing ultracompact quantum algorithms for unbiased quantum simulation.   

Our research also explores directions for new and interesting experiments that can probe fundamentals of quantum many-body states on near-term quantum devices.  I will focus on graph states which have applications in measurement-based quantum computing, quantum networking, and quantum metrology.  We introduce a formalism for their construction as robust quantum states hosting symmetry protected topological order.  We find that certain graph states can be engineered to self-correct unwanted errors.  More generally, I will discuss graph states as important quantum resource states for atomic, molecular, and optical setups. 

Title:    Ultra-Low-Voltage, Beyond CMOS Microelectronics

R. Ramesh, Rice University

Monday, November 7th, 2022
3:00-4:00pm (105 Lin Hall/Zoom Link will be announced).

Abstract:   Despite ever-improving computing efficiency, information technology (IT) represents the fastest growing energy consumer and will have significant implications for U.S. energy consumption. This impending cliff threatens the nation’s ability to solve important problems across science, technology, national security, and energy. Without improvements in computing efficiency, the explosion of the Internet of Things (IoT) and artificial intelligence (AI) applications will exponentially increase energy consumption. A complete rethinking of how computing is performed today is needed to develop the next generation of beyond-CMOS microelectronics. Our scientific mission is built on a core guiding principle that a significant opportunity exists for use-inspired basic science to enable highly energy-efficient computing by exploiting correlated phenomena and consequently lowering the operating voltage. Orders of magnitude improvement in energy efficiency are possible by exploiting correlations (electronic charge/spin and dipolar). We aim to design and manipulate this energy barrier to specifically reduce the operating voltage substantially below what is achievable by today's CMOS technology. This fundamental physics approach to solving systems-level techno-economic problems can lead to dramatically lower energy consumption, in addition to a completely new hierarchy of logic-in-memory information technology building blocks.

Title:    Semiconductor Nanocrystals: from discovery to modern development

Sasha Efros

Tuesday, November 15th, 2022
2:30-3:30pm (105 Lin Hall/Zoom Link will be announced).

Abstract:   Semiconductor nanocrystals (NCs) are the most heavily studied of the nanoscale semiconductors. The size dependence of NC optical properties was discovered independently more than 30 years ago in two different materials: in semiconductor-doped glasses by Ekimov et al (1981), and in aqueous solutions by Brus et al (1983).  I will briefly discuss the history of this discovery, the main obstacles in the development of this field, and the critical breakthroughs along the way.¹

Today, semiconductor NCs have become much more than objects of scientific curiosity. The demonstration of tunable, room-temperature lasing using NC quantum dot solids, the development of NC-based light-emitting diodes and photovoltaic cells, quantum dots TV produced by Samsung, and the first commercial products in the area of NC bio-labeling are just a few illustrations of the broad technological potential of these materials. 

Nonradiative Auger recombination is the central non-radiative relaxation process, which negatively affects the performance of all these devices.  I will discuss why nonradiative Auger recombination is enhanced in NCs, and how we can suppress it.²  

Finally, I am going to discuss the unusual optical properties of the recently discovered CPbX₃ (X=Cl, Br. I) NCs, which are connected with a ground bright exciton state.³ We calculate the lowest quantum confined levels of electrons and holes and the spectra of the allowed optical transitions. The calculations take into account the cubic shape of the perovskite NCs, which results in an inhomogeneous electric field of emitted and absorbed photons.   The symmetry of the ground exciton state has been analyzed, and the radiative decay time has been calculated.   The results of our theoretical calculations have explained the 200 ps radiative decay time and polarization properties measured in experiments on single CsPb(BrCl₂)  quantum dots.

1.     Al. L. Efros and L. E. Brus, ACS Nano 15, 6192–6210 (2021)

2.     Al. L. Efros and D. J. Nesbitt, Nature Nanotech. 11,  661 (2016)

3.      M. A. Becker, R. Vaxenburg, G. Nedelcu, P. C. Sercel, A. Shabaev, M. J. Mehl, J. G. Michopoulos, S. G. Lambrakos, N. Bernstein, J. L. Lyons, T. Stöferle, R. F. Mahrt, M. V. Kovalenko, D. J. Norris, G. Rainò, and Al. L. Efros, Nature, 553, 189 (2018)

Title:   Optical Materials for Far-UV Chiral Sensing and Ultrafast Near-Infrared Optoelectronics

Kevin McPeak, Louisiana State University

Tuesday, December 6th, 2022
2:30-3:30pm (105 Lin Hall).

Abstract:   I will discuss two distinct research thrusts my laboratory has pursued over the last several years, i.e., investigating resonant plasmonic-biomolecular interactions and the emergent optical and electronic properties of noble-transition metal alloys. 

Resonant plasmonic-molecular chiral interactions are a promising route to enhanced biosensing. However, biomolecular optical activity primarily exists in the far-ultraviolet regime, posing significant challenges for spectral overlap with current nano-optical platforms. I will show experimentally and computationally the enhanced chiral sensing of a resonant plasmonic-biomolecular system operating in the far-UV. Our calculations show that detectable enhancements in the chiroptical signals from small amounts of biomolecules are possible only when tight spectral overlap exists between the plasmonic and biomolecular chiral responses. We support this conclusion experimentally by using Al gammadion arrays to enantiomerically discriminate ultrathin (< 10 nm thick) films of Tyrosine. Our results demonstrate the importance of using far-UV active metasurfaces for enhancing natural optical activity.

Noble-transition metal alloys are a new class of materials for interband-driven hot hole generation with NIR light. NIR hot-carrier generation in pure, noble metals suffers from insufficient energy to exceed the interband energy threshold (IET) (e.g.,> 2 eV), and in pure transition metals, rapid hot-carrier thermalization. Band hybridization in select noble-transition metal alloys can overcome these issues, yielding emergent properties that facilitate tuning the hot-carrier distribution and lifetime.

References

1.    Tiago Ramos Leite, Lin Zschiedrich, Orhan Kizilkaya, and Kevin M. McPeak “Resonant Plasmonic–Biomolecular Chiral Interactions in the Far-Ultraviolet: Enantiomeric Discrimination of sub-10 nm Amino Acid Films” Nano Lett. 22, 18, 7343–7350, (2022)

2.    Sara KF Stofela, Orhan Kizilkaya, Benjamin T Diroll, Tiago R Leite, Mohammad M Taheri, Daniel E Willis, Jason B Baxter, William A Shelton, Phillip T Sprunger, Kevin M McPeak, “A Noble-Transition Alloy Excels at Hot-Carrier Generation in the Near Infrared,” Advanced Materials 32 (23), 1906478 (2020)

Title: Site-specific spectroscopic measurement of spin and charge in (LuFeO₃)_m/(LuFe₂O₄)₁  multiferroic superlattices

Janice Musfeldt, University of Tennessee  

Tuesday, February 22, 2022
1:15-2:15pm (Zoom link will be announced)

Abstract:  Interface materials offer a means to achieve electrical control of ferrimagnetism at room temperature as was recently demonstrated in (LuFeO₃)_m/(LuFe₂O₄)₁ superlattices. A challenge to understanding the inner workings of these complex magnetoelectric multiferroics is the multitude of distinct Fe centres and their associated environments. This is because macroscopic techniques characterize average responses rather than the role of individual iron centres. Here, we combine optical absorption, magnetic circular dichroism and first-principles calculations to uncover the origin of high-temperature magnetism in these superlattices and the charge-ordering pattern in the m = 3 member. In particular, interface spectra establish how Lu-layer distortion selectively enhances the Fe2+ → Fe3+ charge-transfer contribution in the spin-up channel, strengthens the exchange interactions and increases the Curie temperature. Comparison of predicted and measured spectra also identifies a non-polar charge ordering arrangement in the LuFe₂O₄ layer. This site-specific spectroscopic approach opens the door to understanding engineered materials with multiple metal centres and strong entanglement.

Title: Searches for New Physics with Quantum Sensors in the Laboratory and in Space

Marianna Safranova, University of Delaware

Tuesday, March 1, 2022
1:15-2:15pm (Zoom link will be announced)

Abstract:  The extraordinary advances in quantum control of matter and light have been transformative for atomic and molecular precision measurements enabling probes of the most basic laws of Nature to gain a fundamental understanding of the physical Universe. Exceptional versatility, inventiveness, and rapid development of precision experiments supported by continuous technological advances and improved atomic and molecular theory led to rapid development of many avenues to explore new physics. I will give an overview of atomic and molecular physics searches for physics beyond the standard model and focus of dark matter searches with atomic and nuclear clocks. Recent ideas on dark matter searches and test of general relativity with clocks in space will be discussed.  I will also briefly discuss new ideas and prototype experiments in gravitational wave detection with atomic quantum sensors.

Title: Bridging Few- And Many-Body Physics in Fermi Gases

Yangqian Yan, The Chinese University of Hong Kong

Friday, March 4, 2022
2:30-3:30pm (Zoom link will be announced)

Abstract:  The strongly interacting Fermi gas with large scattering lengths constitutes a paradigmatic model system that is relevant to atomic, condensed matter, nuclear and particle physics. Such a model applies to the core of nuclei, the crust of a neutron star, and the highly controllable ultracold atoms with tunable scattering lengths. Whereas it is challenging to theoretically tackle strongly interacting Fermi gases, the virial expansion serves as a powerful tool to bridge few- and many-body physics. With the help of Richard Feynman’s path integral, we used classical computers to simulate few-body systems and obtained the viral coefficients for many-body systems. In particular, I will discuss how to extract the so-called contact, the central quantity controlling dilute quantum systems, using the virial expansion. 

Including multiple flavors in interacting Fermi gases provides physicists with an even richer playground. In a recent collaboration with Prof. Gyu-Boong Jo’s group at HKUST, we have theoretically predicted and experimentally verified that the contact of a 3D SU(N) Fermi gas approaches spinless bosons via a particular scaling law at finite temperatures. This provides a rigorous proof of the bosonization of 3D SU(N) fermions and also opens the door to a new framework of manipulating quantum statistics in many-body systems.

Title: A Direct View into Optical Lattices: Dynamics, Topology and Dissipation

Klaus Sengstock,  University of Hamburg

Friday, March 11, 2022
2:30-3:30pm (Zoom link will be announced)

Abstract:  Ultracold atoms in optical lattices act as powerful systems for quantum technologies, including quantum simulation, quantum information and quantum computing, as well as for precision experiments and as fully new model systems. I will report on recent developments from our lab to image 3D optical lattice systems with better than single-site resolution (Nature 599, 571 (2021)) allowing for a direct view into dynamics, thermalization and further properties within the optical lattices. We could observe the spontaneous build-up of a density waves (PRX, in print, arXiv:2108.11917) and study topological properties of quantum gases in lattices (Nature Physics, 15, 449 (2019)).

Title: Using Computational Methods to Improve and Design Energy Materials

MIchelle Johannes, Naval Research Lab

Tuesday, March 22, 2022
1:15-2:15pm (Zoom link will be announced)

Abstract:  Although batteries and fuel cells are generally considered electrochemical systems, a surprising amount of their performance stems from the physics of the materials that make up their basic components:anode, cathode and electrolyte.  Ionic conduction, electronic conductivity, chemical stability and voltage can all be traced back to intrinsic materials properties which are governed by fundamental physics.

In this talk, I will discuss how computational simulation can be used to analyze, develop and improve energy materials, such as  Li-ion batteries, supercapacitors, and fuel cells.  I will specifically discuss how seemingly small details of the electronic structure can make or break  performance.  I will further discuss some of the safety concerns that are currently driving battery research and development and how computational screening can determine in advance how stable a material will be during charging.  Finally, I will discuss the use of nanoscale materials and how they can be stabilized against degradation by judicious oxide coating.

Title:  Photons, plasmons, and polaritons: optical phenomena in quantum materials

Stephanie Law, University of Delaware

Tuesday, March 29, 2022
1:15-2:15pm (Zoom link will be announced)

 Abstract: When light interacts with quantum materials, we can excite a variety of modes including plasmon polaritons and optical phonons. In layered materials, these modes can interact with each other to produce hybrid excitations resulting in novel optical phenomena such as negative refraction, extreme light confinement, and preferential thermal emission. In this talk, I will first discuss our work on the growth of topological insulator thin films and heterostructures by molecular beam epitaxy. Topological insulators have two-dimensional surface states that house massless electrons, and the plasmon polaritons in these materials show unusual properties. I will discuss the dispersion of these modes and show record high mode indices and extremely long polariton lifetimes. Using MBE, we can then grow layered structures comprising multiple topological and normal insulators, resulting in hybrid coupled plasmon modes. We can also grow self-assembled topological insulator quantum dots, which could be used as qubits. I will close by discussing our work on semiconductor hyperbolic metamaterials, which are layered materials comprising alternating metallic and dielectric materials. I will show our work demonstrating strong coupling between the volume plasmon polariton modes and quantum well intersubband transitions.

Title: Emergence and quantum complexity in mono element solids

G. Baskaran, Matscience, IITMadras, Chennai, India

Friday, April 29, 2022
2:30-3:30pm (Zoom link will be announced)

Abstract:  We are witnessing gradual understanding of myriads of materials, synthetic quantum matter and ever growing number of phenomena and surprises. Emergence and quantum complexity are smiling at us. I will point to some of our works and briefly discuss two families: allotropes of carbon and solid hydrogen. Emergence creates a web of unexpected connections and new insights. For example, graphene offers [1,2] relativistic analogue of time dilation, Kaluza Klein collapse, zitterbewegung, parity anomaly, emergent gauge fields, Majorana Fermions etc. Small twists in bilayer graphene produces superconductor or Mott insulator ! Solid hydrogen under pressure takes us through a series of unexpected structures and Mott insulating phases, before becoming a metal that Wigner and Huntington envisaged in 1935.

[1] G. Baskaran, Quantum Complexity in Graphene, Mod. Phys. Lett., B25, 605 (2011)
[2] G. Baskaran, Physics of Quanta and Fields in Graphene,
   in `Graphene: Synthesis, Properties and Phenomena,
   Editors: C.N.R. Rao and A.K. Sood (Wiley)

Title: Connecting the dots

Michael Scheibner, University of California, Merced

Friday, April 15, 2022
2:30-3:30pm (Zoom link will be announced)

Abstract:  How many straight lines connect two dots? The answer: That depends on the dots and their environment. By placing two quantum dots near each other we can probe fundamental quantum mechanical properties of the semiconductor system and its interactions. Equipped with that knowledge we can start to tailor the quantum states to develop novel quantum-enhanced applications. In doing so, we make use of an enhanced versatility and functionality that arises from the superposition of states of the two dots. For example, their discrete electronic states and optical transitions can be tuned in-situ over tens of meV. As a result, it is possible to control and realize coupling between varieties of excitations of the solid-state system, ranging from different spin states, phonons to the mechanical motion of the system. In this seminar I will review the unique properties of coupled quantum dots and discuss their advantages as tools in quantum technologies, such as quantum photonics and quantum sensing.  

Title: Representing many-body quantum states with neural networks

Martin Gärttner, University of Heidelberg

Friday, April 29, 2022
2:30-3:30pm (Zoom link will be announced)

Abstract:  I will discuss the idea of using neural networks a variational ansatz for the quantum many-body wave function. These neural network quantum states have recently been employed for variational ground state search, quantum dynamics, and quantum state tomography. I will report on two contribution of our group on using neural network representations of mixed quantum states for simulating the dynamics of open quantum systems and for quantum state tomography.

Title: TBA

Henri Lezec, NIST

Friday, April 29, 2022
2:30-3:30pm (Zoom link will be announced)

Abstract:  TBA

Title:  TBA

David Ebert, OU

Tuesday, March 29, 2022 

1:15-2:15pm (Zoom link will be announced)

 Abstract: TBA

Title: Representing many-body quantum states with neural networks

Martin Gärttner, University of Heidelberg

Friday, April 29, 2022
2:30-3:30pm (Zoom link will be announced)

Abstract:  I will discuss the idea of using neural networks a variational ansatz for the quantum many-body wave function. These neural network quantum states have recently been employed for variational ground state search, quantum dynamics, and quantum state tomography. I will report on two contribution of our group on using neural network representations of mixed quantum states for simulating the dynamics of open quantum systems and for quantum state tomography.

Title:Quantum fluctuations in nonlinear Schrödinger breathers

O. V. Marchukov, Institut für Angewandte Physik, Technical University of Darmstadt, Germany

Monday May 16, 2022
SPECIAL TIME:  9:00-10:00am   (Zoom link will be announced)

Abstract: Solitons are nonlinear waves that show up in many different fields of physics: From solitary water waves to Langmuir waves in plasmas, the formation of solitons attracts the interest of theoreticians and experimentalists alike. In this talk, we focus on the two-soliton breathers – nonlinear superposition of two bright solitons – in one-dimensional Bose gases that were recently obtained experimentally [2,4]. We present the linearization approach that allows one to evaluate quantum fluctuations of the parameters that define the solitonic solutions.

Furthermore, we demonstrate the uncertainty relations of the parameters for both the fundamental soliton and breather. We also discuss the dissociation of breather under both the influence of an external perturbation [1] and the quantum fluctuations of relative velocity. The former allows us to evaluate the breather dissociation time, i.e. the time it takes for the constituent solitons to be significantly separated. Without an external perturbation, the dissociation does not occur in the mean-field regime, thus making the dissociation time a potentially observable manifestation of quantum effects [3].

References

[1] O. V. Marchukov et al., Phys. Rev. A 99, 063623 (2019).

[2] A. Di Carli et al., Phys. Rev. Lett. 123, 123602 (2019).

[3] O. V. Marchukov et al., Phys. Rev. Lett. 125, 050405 (2020).

[4] D. Luo et al., Phys. Rev. Lett. 125, 183902 (2020).

Title: Probing Fundamental Physics with Precision Molecular Spectroscopy

 Samuel Meek,  Max Planck Institute for Multidisciplinary Sciences, Gaettingen

Monday May 23, 2022
SPECIAL TIME:  9:00-10:00am   (Zoom link will be announced)

Abstract: Precise measurements of molecular transition frequencies can provide a means to test fundamental physical questions, such as whether there are additional forces between the nuclei that are not predicted by the standard model or if the masses of elementary particles vary over time.  Such measurements can also help determine physical constants more precisely and provide data that can be used to better interpret astronomical spectra.  In my lab, we have developed an apparatus for determining vibrational and electronic transition frequencies of isolated small molecules with high precision.  The central component of this apparatus is a precision laser system containing narrow-linewidth reference and spectroscopy lasers linked to each other and to an atomic clock reference using an optical frequency comb.  So far, we have used this apparatus to investigate electronic transitions in OH, OD, and SH, as well as vibrational transitions in HD and D₂.  In all of these measurements, we have been able to determine the absolute transition frequencies with orders of magnitude higher precision than previously reported and, in some cases, detect systematic errors in earlier, less precise measurements.  In future measurements, trapping the molecules and applying quantum techniques can help to achieve narrower transition linewidths and improve the precision further.

Title: High-precision physics and chemistry with ultracold molecules

Tanya Zelevinsky, Columbia University

Tuesday, August 24, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:  Techniques for controlling the internal quantum states and motion of atoms have led to extremely precise metrology and studies of degenerate gases.  Extending such techniques to various types of molecules further enriches the understanding of fundamental physics, basic chemical processes, and many-body science.  Samples of diatomic molecules can be created by binding laser-cooled atoms, or by direct molecular laser cooling.  We explore both approaches and demonstrate high-precision metrology with an optical-lattice based molecular clock as well as chemistry in the highly nonclassical domain.

Title: Topological physics: from photons to electrons

Mohammad Hafezi, University of Maryland

Friday, September 3, 2021
12:15-1:15pm (Zoom link will be announced)

Abstract:  here are many intriguing physical phenomena that are associated with topological features --- global properties that are not discernible locally. The best-known examples are quantum Hall effects in electronic systems, where insensitivity to local properties manifests itself as conductance through edge states which are insensitive to defects and disorder. In the talk, we first discuss how similar physics can be explored with photons; specifically, how various topological models can be simulated in various photonics systems, from ring resonators to photonic crystals. We then discuss that the integration of strong optical nonlinearity can lead to unique bosonic phenomena, such as topological frequency combs, topological source of quantum light, and chiral quantum optics. These results may enable the development of classical and quantum optical devices with built-in protection for next-generation optoelectronic and quantum technologies. In the end, we discuss an emerging field at the interface of quantum optics and correlated electron systems, with the goal of creating and manipulating many-body states of light-matter hybrids with new functionalities, such as high-Tc superconductors.  

Title:   Synthetic dimensions in ultracold quantum matter

Kaden Hazzard, Rice University

Tuesday, September 7, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:  A synthetic dimension is a degree of freedom where motion in space is mimicked by motion through other states, such as hyperfine states of atoms or rotations of molecules. These states act as lattice sites in extra spatial dimensions, and can be used alone or in combination with any real spatial dimensions. The superb control of internal degrees of freedom opens a vast new frontier in quantum science, both for simulating phenomena in condensed matter (such as topological band structures or fracton matter) and for studying phenomena that don't occur elsewhere in nature, such as fluctuating quantum strings, embranes, and even 3-branes that fluctuate in 4D. 

In this talk I will discuss our theoretical understanding of synthetic dimensions, and the rapid experimental progress exploring synthetic dimensions made with three types of ultracold matter: Rydberg atoms, molecules, and momentum-space lattices. 

Title:  Simulating many-body physics using quantum tensor networks

Michael Foss-Feig, Honeywell

Friday, September 17, 2021
12:15-1:15pm (Zoom link will be announced)

Abstract:  Tensor network techniques exploit the structure of entanglement to dramatically reduce the difficulty of simulating quantum systems on classical computers. But these techniques have limitations, and many problems in many-body quantum physics, for example simulating dynamics, remain intractable despite decades of effort to solve them.  Quantum computers offer an alternative route to simulating quantum systems that is in principle efficient, but their small size and limited fidelities have so far prevented solution of problems of real practical interest that cannot be solved classically.  Here we discuss prospects for combining these two techniques by directly representing tensor-network states as quantum circuits, and show that recent developments in quantum hardware make it possible to carry out quantitatively accurate simulations of quantum dynamics directly in the thermodynamic (infinite system size) limit using a small number of qubits.

Title: Entangled Bose-Einstein condensates in momentum space

Carsten Klempt, Leibniz University Hannover

Tuesday, September 21, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:  The generation and application of entangled many-particle states is a central goal of the second quantum revolution. In our work, we employ spin-changing collisions to create spin entanglement in atomic Bose-Einstein condensates. I will present our work towards transferring this entanglement towards external degrees of freedom. The successful transfer of spin entanglement to momentum states presents an important step towards the operation of future atom interferometers with a sensitivity beyond the Standard Quantum Limit.

Title: Dipolar Quantum Gases of Magnetic Lanthanide Atoms: achievements and future opportunities

Francesca Ferlaino, University of Innsbruck

Tuesday, September 28, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:   Since its creation, the field of ultracold atoms has been through fantastic developments. Some of the most recent include the development of quantum-gas microscopes, atom tweezers, and various forms of interaction engineering. Each of these experimental advances has allowed new quantum phenomena to be accessed and observed. A further important development is based on the use of more exotic atomic species, whose peculiar atomic properties have allowed to broaden the horizons of investigation.

This talk aims to retrace the new opportunities that have emerged from the use of quantum gases composed of the strongly magnetic erbium and dysprosium atoms from the perspective of the Innsbruck experiments.
Thanks to their large magnetic moment, these species exhibit a large dipolar interaction that has allowed us to observe rotonic excitations, quantum droplets, and supersolid states. Moreover, their dense atomic spectrum has also made possible to implement new optical manipulation schemes, and more recently the observation of an Hz-wide transition in the telecom frequency region promises new possibilities in quantum optics.

Title: Observation of a Transition between Dynamical Phases in a Quantum Degenerate Fermi Gas

Joseph Thywissen, University of Toronto

Tuesday, October 5, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:   I will discuss collective dynamics of ultracold fermions, in two contexts. First, I will discuss a study of spin dynamics near the non-interacting point of an s-wave Feshbach resonance. The collective enhancement of weak interactions allows for an interesting range of behaviors, including a non-equilibrium phase transition. Second, I will discuss a proposal to study collective orbital dynamics of spin-polarized fermions in an optical lattice.

A proposed paradigm for out-of-equilibrium quantum systems is that an analogue of quantum phase transitions exists between parameter regimes of qualitatively distinct time-dependent behavior. We present evidence of such a transition between dynamical phases in a cold-atom quantum simulator of the collective Heisenberg model. Our simulator encodes spin in the hyperfine states of ultracold fermionic potassium. Atoms are pinned in a network of single-particle modes, whose spatial extent emulates the long-range interactions of traditional quantum magnets. We find that, below a critical interaction strength, magnetization of an initially polarized fermionic gas decays quickly, while above the transition point, the magnetization becomes long-lived, due to an energy gap that protects against dephasing by the inhomogeneous axial field. Our quantum simulation reveals a non-equilibrium transition predicted to exist but not yet directly observed in quenched s-wave superconductors. 

In the second part of the talk, I discuss non-equilibrium orbital dynamics of spin-polarized ultracold fermions in the first excited band of an optical lattice. A specific lattice depth and filling configuration is designed to allow the px and py excited orbital degrees of freedom to act as a pseudo-spin. Bragg dressing can reduce single-particle dispersion rates, such that a collective many-body gap is opened with only moderate Feshbach enhancement of p-wave interactions. Time permitting, I will discuss the first experimental steps towards realizing this proposal. 

Title: A quick visit to the world of quantum graphs

Alejandro Chávez-Domínguez, OU Mathematics

Friday, October 15, 2021

12:15-1:15pm (Zoom link will be announced)

Abstract:  A classical graph consists of a set of vertices, some pairs of which are joined by edges. In contrast, a quantum graph is a linear space of square matrices with complex entries, containing the identity matrix and closed under taking the conjugate transpose. This seemingly strange notion has its origins in Quantum Information Theory, where such objects play a role that in  classical Information Theory is occupied by a classical graph.

In the talk I will explain the analogy relating classical and quantum graphs, and will present a couple of examples of recently-developed quantum versions of some geometric notions from classical graph theory. Based on joint works with Andrew Swift.

Title: Site-specific spectroscopic measurement of spin and charge in (LuFeO₃)_m/(LuFe₂O₄)₁ multiferroic superlattices

Janice Musfeldt, University of Tennessee

Tuesday, October 26, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:  TBA

Title: Heralded Noiseless Amplification and Attenuation for Quantum Communications

Todd Pittman,  UMBC

Tuesday, November 2, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:  Although quantum optical signals cannot be deterministically amplified without adding noise, it has recently been shown that non-deterministic (heralded) noiseless amplification is possible.   Somewhat surprisingly, the inverse process of heralded noiseless attenuation has also been shown to be useful in the context of quantum communications. Here we review our group’s recent work in these areas, including the counterintuitive use of an Optical Parametric Amplifier (OPA) as an attenuator, and methods of combining heralded amplifiers and attenuators to reduce the amount of “which path” information left behind in a quantum communications channel. Many of these interesting effects result from the probabilistic nature of the heralding process, and are closely related to the idea that the “annihilation” operator, â, can actually increase the average number of photons for certain states.

Title: The Quantum Neutron

Charles Clark, NIST, JQI and Univ. of Maryland

Date: Friday, November 5, 2021
12:15-1:15pm LH 105 

Abstract:   I present a simple overview of the particle and wave properties of the neutron, with emphasis on their parallels in light, electrons and atoms. Neutron interferometry enables one to realize the quantum limit of the Young double slit experiment, when no mor that only neutron is ever present in the interferometer. How can only one neutron go through both slits? We have used neutron interferometry and holography to address some of the questions of structured waves of light and matter that have been studied with photons, electrons and atoms.​

Title: Lattice resonances: a collective response of periodic arrays of nanostructures

Alejandro Manjavacas,  Instituto de Óptica ( CSIC)/University of New Mexico.

Tuesday, November 9, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:  Periodic arrays are an exceptionally interesting arrangement for nanostructures due to their ability to support strong collective lattice resonances, which arise from the coherent multiple scattering enabled by the array periodicity. Thanks to these exceptional properties, periodic arrays are being exploited in a wide variety of applications, including ultrasensitive biosensing, nanoscale light emission, and color printing, to cite a few. 


The goal of this seminar is to provide an instructive introduction to this topic. To that end, we will start by discussing how the interplay between the response of the individual constituents of the array and their collective interaction determines the ultimate limits of the field enhancement provided by a periodic array. We will also discuss the response of arrays with multi-particle unit cells using an analytical approach based on hybridization theory, which provides a simple and efficient way to design periodic arrays with engineered properties. We will pay particular attention to bipartite arrays and show how, depending on the relative position of the particles within the  unit cell, these systems can support super- or subradiant lattice resonances with very different optical responses.

Title: Unsupervised Machine Learning of Quantum Phase Transitions

 Zhe-Xuan Gong, Colorado School of Mines

Tuesday, November 16, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:    Experimental quantum simulators have become large and complex enough that discovering new physics from the huge amount of measurement data can be quite challenging, especially when little theoretical understanding of the simulated model is available. Unsupervised machine learning methods are particularly promising in overcoming this challenge. I will review typical unsupervised learning methods and show that they generally only work for learning simple symmetry-breaking quantum phase transitions. I will then show that a more advanced method known as diffusion map, which performs nonlinear dimensionality reduction and spectral clustering of the measurement data, has much better potential for unsupervised learning of complex phase transitions, such as topological phase transitions and many-body localization. This method is readily applicable to many experimental quantum simulators as it only requires measuring each particle in a single and local basis.

Reference: A. Lidiak and Z.-X. Gong, Phys. Rev. Lett. 125, 225701 (2020).

Title:  Quantum Control with Spinor Bose-Einstein Condensates 

Hillary Hurst, San Jose State University

Friday, November 19, 2021
12:15-1:15pm (Zoom link will be announced)

 Quantum Control with Spinor Bose-Einstein Condensates 

Abstract: Understanding and controlling many-body quantum systems in noisy environments is paramount to developing robust quantum technologies. An external environment can be thought of as a "measurement reservoir" which extracts information about the quantum system. Cold atoms are well suited to examine system-environment interaction via weak (i.e. minimally destructive) measurement techniques, wherein the measurement probe acts as the environment and also provides a noisy record of system dynamics. The measurement record can then be used in a feedback scheme, opening the door to real time control of quantum gases. In this talk I discuss our theoretical proposal to use weak measurement and feedback to engineer new phases in spin-1/2 Bose-Einstein condensates. First, I will discuss the formalism we developed to describe condensates undergoing weak measurement via phase-contrast imaging. We then show that measurement and feedback alters the effective Hamiltonian governing system dynamics, thereby driving phase transitions reminiscent of a quantum quench for the closed system. We also develop a feedback cooling protocol which prevents runaway heating of the condensate due to measurement backaction. Our results show that measurement and feedback can alter condensate dynamics in a stable, controllable manner and provides a route toward Hamiltonian engineering in many-body systems. 

HMH, S. Guo, and I. B. Spielman, Physical Review Research, 2(4), 043325 (2020), HMH and I. B. Spielman, Physical Review A 99.5, 05361 (2019) 

Title: Formation and Evolution of Single Molecule Junctions Containing ransition Metal Atoms

Maria Kamanetska, Boston University

Tuesday, November 30, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:  Untangling structure-function relationships on the nano-scale is critical to understanding biological molecular machinery and to engineering human-made nano-devices. In this talk I will give an overview of my lab’s approaches to probing and controlling sub-nanometer atomic arrangements in biological and synthetic systems. I will focus on our combined Scanning Tunneling Microscope-based Break Junction measurements and Density Functional Theory studies of the formation and evolution of molecular junctions incorporating transition metal atoms.  Such junctions can increase the scope of observable phenomena due to incorporation of metal centers with new degrees of freedom. Overall, our methods allow a comprehensive, atomic picture of junction structure and electronic properties. Interestingly, we find that transition metal centers can be wired into single molecule junctions by coordinating to organic linkers during junction elongation. These in situ assembled coordination complexes present a new approach for creating molecular junctions with potential for non-trivial electronic and spin functionality.

Title: Quantum Error Correction Now!

Kenneth Brown, Duke University

Tuesday, December 7, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract:   The power of quantum computers requires reliable and robust quantum systems.  It is widely believed that quantum error correction will be critical to make quantum operations with errors less than one part per billion. In this talk, I will explain the basics of quantum error correction and then discuss recent experimental demonstrations showing that the time for quantum error correction is now.

Title: Advanced laser development for uses in fundamental research into the Standard Model, quantum computation, and to the highest powers in industry

Dawn Meekhof, Lockheed Martin Laser and Sensor Systems

Friday, February 12, 2021
12:15-1:15pm (Zoom link will be announced)

Abstract: Laser technology grew out of advanced pure research, and has proven to be an excellent new tool for many fields. My career has required developing new lasers for fundamental research into the Standard Model, for quantum computation, atomic clocks, advanced telecom products, medical devices, and defense systems. For some of this work, reaching an exact wavelength with 1 mW was necessary, for others building a massive system with 100kW. My career path has taken the laser technology from working to answer the most fundamental of scientific questions to practical applications in industry. In this talk, I will discuss the laser technology, the research, the applications, and how a scientific career in our world can evolve. 

Title: Room temperature polaritonics in all-inorganic cesium lead halide perovskite

Carole Diederichs, Physics Laboratory of the Ecole Normale Supérieure (LPENS), Sorbonne University.

Tuesday, February 16, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract: Strong light-matter coupling in microcavities of various dimensionalities and the resulting hybrid exciton-photon quasiparticles, i.e. the exciton-polaritons, have been reported in a wide range of organic and inorganic semiconductors. While demonstrations of the polariton Bose-Einstein condensation, which is at the heart of promising applications such as polariton lasers, all-optical polaritonic circuits or polariton quantum simulators, are limited within a handful of semiconductors at both low and room temperatures. In inorganic materials, polariton condensation significantly relies on sophisticated epitaxial growth, while organic active media usually suffer from large threshold density and weaker nonlinearities. In this respect, strong efforts have been done in hybrid organic-inorganic perovskite materials, as they combine the advantages of both inorganic and organic materials. However, up to now, polariton condensation has not been observed in such materials. The all-inorganic cesium lead halide perovskites are now part of a class of materials that are drawing attention for polaritonics at room temperature. The epitaxy-free fabrication combined with their excellent optical gain properties, their tunable emission from UV to NIR, and their better optical stability under high laser flux illumination compared with hybrid perovskites, promise further important technological developments. In this seminar, I will present our first results on polariton condensation at room temperature in all-inorganic perovskite microplatelets embedded in planar microcavities, which opened the way to the demonstration of polariton condensates propagation in perovskite microwires and polariton condensation in perovskite lattices that will be also presented. These realizations in epitaxy-free wavelength-tunable materials advocates the great promise of perovskite for polaritonics applications.

Title: Chip-scale electrically-pumped optical frequency combs

Lukasz Sterczewski, JPL

Tuesday, February 23, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract: Chip-scale optical frequency combs (OFC) merge the concept of spectrally broadband emission with coherent laser radiation in a compact footprint. Hundreds to thousands equidistant phase-locked lines synchronized by intracavity nonlinearities have found many applications ranging from telecommunication to optical sensing. To date, however, most developments have been made in the near-IR region at telecom wavelengths. The mid-IR region above 3 µm of wavelength is particularly attractive for optical sensing of hydrocarbons associated with the existence of life. Unfortunately, mid-IR wavelengths still pose a technological challenge and limit the number of available OFC platforms.

One of the efficient ways to generate mid-IR OFCs is to exploit inherent nonlinearities in semiconductor lasers. In this seminar, we will discuss recent progress in interband cascade laser (ICL) OFCs. These sources analogous to that used in the tunable laser spectrometer (TLS) have shown excellent OFC properties with great suitability for free-running dual-comb spectroscopy. The same ICL material has also been used for fabricating GHz-bandwidths room-temperature photodetectors to demonstrate a self-contained room-temperature dual-comb spectrometer. The seminar will also briefly cover mid-IR diode laser OFCs, which have recently extended the portfolio of electrically-pumped OFCs.

Bio: Dr. Lukasz Sterczewski has been a NASA Postdoctoral Program (NPP) research fellow in the Microdevices Laboratory at JPL (389R) since 2019. At MDL, he was responsible for device testing and characterization to optimize the spectral properties of interband cascade laser frequency combs. His doctoral work conducted in the PULSE laboratory at Princeton University, and THz laboratory at Wroclaw University of Science and Technology, Poland, focused on frequency comb spectroscopy in the presence of excessive amounts of noise and unstabilized operation of semiconductor laser sources.

Title:  Atom-based storage and manipulation of electromagnetic signals: a cold-atom quantum memory and a room-temperature atomic radio

Lindsay LeBlanc, University of Alberta.

Friday, March 5, 2021 
12:15-1:15pm (Zoom link will be announced)

Abstract: The ability to store and manipulate quantum information encoded in electromagnetic (often optical) signals represents one of the key tasks for quantum communications and computation schemes. In this talk, I will discuss two platforms our group is using to manipulate electromagnetic signals with atoms:  With a cold-atom system, we have developed and characterized an efficient and broadband quantum memory that operates in a regime that makes use of Autler-Townes splitting (ATS). We demonstrate on-demand storage and retrieval of both high-power and less-than-one-photon optical signals with total efficiencies up to 30%, using the ground state spin-wave as our storage states. We also realize a number of photonic manipulations, including temporal beamsplitting, frequency conversion, and pulse shaping.  In a second, a room-temperature atomic vapour system, we have developed a scheme for radio signal transduction between a microwave and an optical carrier, all mediated through the atoms with the help of a resonant microwave cavity.  We are further exploring this promising atomic-vapour + microwave-cavity platform for applications related to optical quantum memory and quantum sensing.

Title: Commercialising Silicon Quantum Computers

James Palles-Dimmock, Quantum Motion

Friday, March 12, 2021

12.15-1.15pm (Zoom link will be provided)

Abstract: Given that the highest impact applications of quantum computers will need a million plus qubits, how can we get there as quickly as possible? In this talk I will summarise the key hurdles that need to be overcome in order to realise a scalable quantum processor and describe Quantum Motion’s approach. Quantum Motion is developing a quantum processor based on gate defined quantum dot spin qubits in silicon, I will contrast this with other approaches and highlight the particular benefits of our approach and some of our most recent published results.

Title: Predicting the properties of Ga₂O₃ using first-principles calculations

Hartwin Peelaers, University of Kansas

Tuesday, March 23, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract: Gallium oxide (β-Ga₂O₃) is a promising material for high-power electronic devices, as it combines excellent material properties with ease of mass production. It is a wide-band-gap semiconductor (band gap of 4.8 eV) with a monoclinic crystal structure. Its high carrier mobility and large band gap have attracted a lot of attention for use in high-power electronics and transparent conducting applications. 

These applications require the presence of large concentrations of free carriers. Based on first-principles calculations using hybrid functionals, I will discuss different approaches to efficiently create free carriers in Ga₂O₃. Their presence can lead to additional light absorption, both through direct absorption, but also through phonon- or defect-mediated indirect absorption. Both types of absorption give rise to distinct absorption features, which have been observed recently. Finally, I will discuss how calculations can give insights in various methods to tailor the properties of Ga₂O₃.

Title: TBD
Qiang Lin, Electrical and Computer Engineering, University of Rochester

Tuesday, March 30, 2021
1:15pm-2:15pm (Zoom link will be announced)

Title: Single-, few-, and many-photon physics in mesoscopic atomic chains
Ana Asenjo-Garcia, Columbia University 

Friday, April 9, 2021
12:15pm-1:15pm (Zoom link will be announced)

Abstract: Tightly packed ordered arrays of atoms (or, more generally, quantum emitters) exhibit remarkable collective optical properties, as dissipation in the form of photon emission is correlated. In this talk, I will discuss the single-, few- and many-body out-of-equilibrium physics of 1D arrays, and their potential to realize versatile light-matter interfaces. For small enough inter-atomic distances, atomic chains feature dark states that allow for dissipationless transport of photons, behaving as waveguides for single-photon states. Atomic waveguides can be used to mediate interactions between impurity qubits coupled to the array, and allow for the realization of multiple paradigms in waveguide QED, from bandgap physics to chiral quantum optics. Due to the two-level nature of the atoms, atomic waveguides are a perfect playground to realize strong photon-photon interactions. At the many-body level, I will address the open question of how the geometry of the array impacts the process of “Dicke superradiance”, where fully inverted atoms synchronize as they de-excite, emitting light in a burst (in contrast to the exponential decay expected from independent emitters). While most literature attributes the quenching of superradiance to Hamiltonian dipole-dipole interactions, the actual culprits are dissipative processes in the form of photon emission into different optical modes. I will provide an understanding of the physics in terms of collective jump operators and demonstrate that superradiance survives at small inter-atomic distances. I will finish my talk by discussing the implications of correlated photon emission for quantum information processing and metrology.

Title:  Colloidal Semiconductor Nanocrystals: (Un)Conventional and Quantum Materials and Devices

Cherie R. Kagan, University of Pennsylvania, Departments of Electrical and Systems Engineering, Materials Science and Engineering, and Chemistry

Tuesday, April 13,  2021
1:15-2:15pm (Zoom link will be announced)

Abstract: Colloidal semiconductor nanocrystals (NCs) are typically 2-20 nm diameter fragments of the bulk solid. They are known as “artificial atoms” since electrons, holes, and excitons are quantum-mechanically confined and occupy discrete electronic states. Advances in wet-chemical synthetic methods enable the preparation of NCs tailorable in size, shape, composition, and surface chemistry. As colloids, these NCs are readily dispersed in solvents and deposited using solution-based methods. They can self-assemble to form glassy or crystalline NC solids or be directed to assemble to deterministically position single or countable numbers of NCs. I will focus on routes to design solid-state NC materials by manipulating the NC surface chemistry to strengthen electronic coupling, by exchanging the ligands used in synthesis for more compact chemistries, and NC doping, by introducing atoms and ions that serve as impurities or modify stoichiometry. Ultimately, I will connect NC material design to their physical properties and their application in (un)conventional electronic and optoelectronic devices. I will also give an outlook on the opportunity to exploit NCs as platforms for quantum information science, in particular as optically addressable qubits.

Title: Imaging and time-stamping optical photons with nanosecond resolution for QIS applications

Andrei Nomerotski, BNL

Friday, April 16, 2021
12:15-1:15pm (Zoom link will be announced)

Abstract: I will discuss fast optical cameras based on the back-illuminated silicon sensor and Timepix3 ASIC. The sensor has high quantum efficiency and the chip provides ns scale resolution and data-driven readout with 80Mpix/sec bandwidth. The intensified version of the camera is single photon sensitive and since recently has been used for registration of entangled photons in long-distance quantum networks and for a variety of quantum imaging experiments as well as for other applications such as imaging mass spectroscopy, time-resolved neutron detection and lifetime imaging. I will show recent results focusing on the quantum applications and will discuss possible future directions for the technology.

Title: Non-equilibrium phenomena of ultracold quantum gasses trapped in optical lattice potentials

Charles Brown, UC Berkeley

Tuesday, April 20, 2021
1:15-2:15pm (Zoom link will be announced)

Abstract: Experiments with quantum gasses trapped in optical lattices, an analog of particles in a solid crystalline lattice, shed light on the behavior of condensed-matter systems, including solid-state materials.  Studying non-equilibrium phenomena of quantum gasses in optical lattices provides a method to explore how a lattice’s energy band structure is augmented by inter-particle interactions (band renormalization). Separately, studying such phenomena provides a method to explore the geometric and topological structure of a lattice’s energy bands. These studies are aided by experimental probes that are unavailable to solid-state systems.

In the first part of my talk, I will describe our recent work towards understanding the effects of frustration in a system of bosonic atoms trapped in a unique lattice made of light – an optical kagome lattice. Here, we create a Bose-Einstein condensate, accelerate it, then trap it in the lattice. In doing so, we probe a special energy band of the lattice, which is expected to be dispersionless (flat, as a function of quasimomentum). However, our measurements show that interactions between atoms reintroduce band curvature by deforming the lattice away from the kagome geometry. In the second part of my talk, I will describe our current effort to understand the geometric and topological properties of energy bands, by using a new technique to explore singularities at touching points between two bands.

Title: A quick visit to the world of quantum graphs CANCELED!!!!

Alejandro Chávez-Domínguez, OU

Friday, April 30, 2021

12:15-1:15pm (Zoom link will be announced)

Abstract: A classical graph consists of a set of vertices, some pairs of which are joined by edges. In contrast, a quantum graph is a linear space of square matrices with complex entries, containing the identity matrix and closed under taking the conjugate transpose. This seemingly strange notion has its origins in Quantum Information Theory, where such objects play a role that in  classical Information Theory is occupied by a classical graph.

In the talk I will explain the analogy relating classical and quantum graphs, and will present a couple of examples of recently-developed quantum versions of some geometric notions from classical graph theory. Based on joint works with Andrew Swift.

THIS EVENT IS HOSTED BY CQRT STUDENTS

Title: Catching the wave: preparing for the "quantum decade"

Travis Scholten, IBM Quantum

Tuesday, May 4, 2021

1:15-2:15pm (Zoom link will be announced)

Abstract: Over the past 5 years, quantum computing has migrated out of the lab, and into the world. Over the next 10 years, it is anticipated that advances in this technology will enable quantum computers to become part of enterprise-scale computing workloads. I discuss some near-term applications of quantum computers, connect them to business-relevant problems, and explore how proposed roadmaps for scaling quantum technology necessitate collaborations of people from a wide variety of backgrounds, including those in quantum networking. Finally, I share perspective on my own journey to the industry, lessons learned, and what most excites me about the coming quantum decade.

Title: Exciton-polarons in two-dimensional hybrid lead halide perovskites
Ajay Kandada, Wake Forest University

Friday, August 28th, 2020
12:00-1:00pm (Zoom link will be announced)

Excitonic interactions in 2D semiconductors garner considerable attention due to their relevance in quantum opto-electronics and due to the richness of their physics. Quantum-well like derivatives of organic-inorganic perovskites are emerging material systems where strongly bound two-dimensional excitons have been observed even at room temperature [1,2]. These hybrid semiconductors feature complex lattice dynamics due to the ‘softness’ arising from non-covalent bonds between molecular moieties and the inorganic network and due to the ionic character of the crystal [3]. I will discuss the profound and unique consequences of such dynamic structural complexity on the fundamental character of primary photo-excitations. I will present evidence of polaronic effects [4] and multi-body correlations [5,6], both of which are strongly affected by the lattice dynamics, based on various ultrafast optical spectroscopies.

References

[1]    S. Neutzner, F. Thouin, D. Cortecchia, A. Petrozza, C. Silva and A. R. S. Kandada, Physical Review Materials (2018), 2, 064605.

[2]    F. Thouin et al, Chemistry of Materials (2019), 31, 7085. 

[3]    F. Thouin et al, Nature Materials (2019), 18, 349-356. 

[4]    A. R. S. Kandada and C. Silva, The Journal of Physical Chemistry Letters (2020), 11, 3173.

[5]    F. Thouin, D. Cortecchia, A. Petrozza, A. R. S. Kandada and C. Silva, Physical Review Research (2019), 1, 032032.

[6]    F. Thouin et al, Physical Review Materials (2018), 2, 034001.

Title: Using photons for quantum information
Elizabeth Goldschmidt, University of Illinois

Friday, September 4th, 2020
12:00-1:00pm (Zoom link will be announced)

I will give an overview of recent, ongoing, and future work using coherent atomic and atom-like optical emitters to build quantum light-matter interfaces. Optical fields play an important role in virtually all schemes for interconnected quantum information systems since only optical photons are well-suited for carrying quantum information at room temperature. I will discuss different physical platforms that can form the basis for quantum light-matter interfaces, different modalities of light-matter entanglement for various applications in quantum information science, and the tradeoffs related to these different systems. I will include recent experimental results efficiently generating high-fidelity single photons, investigating the role of inhomogeneity in ensemble-based quantum memory, and developing a new integrated photonic platform with highly coherent emitters. 

Title: Quantum Techniques for Radar Applications
Alberto Marino, University of Oklahoma

Friday, September 11th, 2020
12:00-1:00pm (Zoom link will be announced)

Quantum resources offer the possibility of enhancing the sensitivity of devices beyond the classical limit.  This has led to the proposal and implementation of a number of different techniques that can take advantage of quantum effects for applications that range from computing to imaging to sensing. Among possible applications, radar has emerged as a candidate for quantum enhancement, with recent proof-of-principle experiments showing the viability of quantum radar. In this talk I will give an overview of quantum techniques that might find their way into radar applications. In particular, I will present the basics for techniques such as quantum illumination, quantum-enhanced positioning, and quantum-enhanced clock synchronization. I will discuss the conditions under which they could lead to a quantum-based enhancement for radar applications and their limitations. Finally, I will give an overview of some recent experimental implementations of quantum radars.

Title:  From mechanical entanglement generation to microwave quantum illumination
Shabir Barzanjeh, Institute for Quantum Science and Technology,
University of Calgary.

Friday, September 18th, 2020 
12:00-1:00pm (Zoom link will be announced)

The recent interest in mechanical quantum systems is driven not only by fundamental tests of quantum gravity but also to develop a new generation of hybrid quantum technologies. Here I confirm the long-standing prediction that a parametrically driven mechanical oscillator can entangle electromagnetic fields. We observe stationary emission of path-entangled microwave radiation from a micro-machined silicon nanostring oscillator, squeezing the joint field operators of two thermal modes by 3.40 (37) ~ dB below the vacuum level. This entanglement can be used to implement Quantum Illumination. Quantum illumination is a powerful sensing technique that employs entangled photons to boost the detection of low-reflectivity objects in environments with bright thermal noise. The promised advantage over classical strategies is particularly evident at low signal photon flux. This feature makes the protocol an ideal prototype for non-invasive biomedical scanning or low-power short-range radar detection. We experimentally demonstrated quantum illumination at microwave frequencies. We generate entangled fields using a Josephson parametric converter at millikelvin temperatures to illuminate at room-temperature an object at a distance of one meter. These results are experimental proof-of-principle of bistatic radar setup.

Title: Radar: What is it Good for?
Justin Metcalf, University of Oklahoma

Tuesday, September 22nd, 2020
1:15-2:15pm (Zoom link will be announced)

Radar is an active sensing modality exploiting the radio frequency portion of the electromagnetic spectrum, with deployed systems typically operating at center frequencies from 3 MHz to 100 GHz. Radar technology is a diverse ecosystem driven by phenomenology, application, and technology. This talk will give a broad overview to radar technology, including example applications, dominating constraints/tradeoffs, and some current hot research areas. We will also highlight some of the radar technology being developed at the OU Advanced Radar Research Center (ARRC). The goal of this talk is to provide broad background on the motivations underpinning radar applications and technologies in order to stimulate conversation on the benefits quantum technology can offer to improve radar performance. This talk will be primarily oriented from a signal processing perspective, in order to complement the perspective being offered by Dr. Ruyle in a future talk.

Title: Topological Phase Transitions in Hofstadter-Chern Insulators
Luiz Henrique Santos, Emory University

Friday, October 2nd, 2020
12:00-1:00pm (Zoom link will be announced)

Chern bands are the building blocks of the Hofstadter spectrum when a magnetic flux of order h/e penetrates the unit cell of the 2D lattice. They give rise to quantum Hall phases beyond the Landau level paradigm, which have attracted considerable interest in recent years. Furthermore, rapid progress in the fabrication of superlattices with nanometer scale unit cells has recently led to the experimental realization of integer and fractional Hofstadter-Chern insulators, opening remarkable prospects to explore the non-trivial interplay of lattice effects and electronic topology. In this talk, I will present a framework to classify topological phase transitions between integer and fractional Hofstadter-Chern insulators in graphene superlattices, which are tuned by changing hopping parameters in a fixed background uniform magnetic field. Despite the well-known intricacies of the Hofstadter spectrum, I will discuss how certain universal properties of the topological phase transitions can be identified from a simple analytical function, in particular, the emergence of multi-component Dirac fermions that mediate large transfers of Chern number between critical bands. Furthermore, I will discuss a non-trivial relationship between the energy scale of topological phase transitions and the presence of van Hove singularities in the Hofstadter-Chern bands, which provides an understanding for the origin of these topological phase transitions.

Title: Designing materials at the nanoscale
Pawel Hawrylak, Chair in Quantum Theory of Materials, Nanostructures and Devices, Department of Physics, University of Ottawa

Tuesday, October 6th, 2020
1:15pm-2:15pm (Zoom link will be announced)

We describe challenges and opportunities in condensed matter and materials physics applied to information and communication, lighting and energy technologies. We show how materials designed at the nanoscale address some of these challenges.  These include quantum circuits based on electron spin [1], synthetic quantum systems hosting macroscopic quantum states [2,3], quantum dots in topological insulators [4], semiconductor nanocrystals [5], graphene and 2D materials quantum dots [6-8] and 2D materials for  valley polarized electron gas [8,9] and laser cooling [10].

1. C-Y. Hsieh, et al., Rep. Prog. Phys. 75, 114501 (2012).
2. Blazej Jaworowski et al., Nature Scientific Reports 7, 5529 (2017).
3. B. Jaworowski et al., ”Quantum bits with macroscopic topologically protected states in semiconductor devices”, Special Issue, Quantum Physical Informatics, D.Ferry, Editor, Applied Science 2019, 9, 474; doi:10.3390/app9030474.
4. M. Korkusinski, et al., Nature Scientific Reports 4, 4903(2014).
5. Fengjia Fan, et. al.  Nature 544, 75 (2017).
6. D.Guclu, et. al. ”Graphene Quantum Dots”, Springer-Verlag (2014).
7. Y. Saleem, et. al.,  Journal of Physics: Condensed Matter 31 (30), 305503 (2019).
8. L.Szulakowska, et al, Phys. Rev. B 2020 (submitted).
9. T. Scrace, et al., Nature Nanotechnology 10, 603 (2015).
10. J. Jadczak, et al., Nature Comm: DOI/10.1038/s41467-018-07994 (2019).

Title: Quantum sensors and their networks as exotic field telescopes in multi-messenger astronomy
Andrei Derevianko,  University of Nevada, Reno

Friday, October 16th, 2020
12:00pm-1:00pm (Zoom link will be announced)

In my talk, I will focus on  exotic bosonic fields potentially sourced by powerful astrophysical events, such as binary neutron star and binary black hole  mergers. Because such hypothetical fields are predicted to feebly interact with standard model particles and fields,  we propose to employ precision quantum sensors to detect potential bursts of such exotic fields. We show that to unambiguously correlate such bursts with gravitational wave triggers, the fields must be ultralight and ultrarelativistic. Moreover, networks of precision sensors are required to resolve the progenitor position in the sky thereby establishing a crucial coincidence with the more conventional, e.g., electromagnetic or gravitational wave, observations of the source.  We show that within certain models,  atomic clocks and magnetometers can be sensitive to intense bursts of exotic fields  from astrophysical sources within the reach of current gravitational wave observatories. This opens an intriguing possibility for a novel, exotic physics, modality in multi-messenger astronomy.

Title:  Forging next generation materials through atomic layer engineering 

Derek Meyers, Oklahoma State University

Friday, October 23,  2020
12:00-1:00pm (Zoom link will be announced)

Abstract: Pulsed laser deposition is an emergent synthesis technique that allows stacking of single atomic layers of disparate materials with sharp interfaces and high crystalline quality. In this talk, advanced synchrotron X-ray characterization will be introduced as a powerful tool for investigating the strongly entangled lattice, orbital, charge, and magnetic degrees of freedom exhibited by these nanoscale interfaces. Some of the fascinating physical phenomena derived from strongly correlated electrons will be showcased as paragons of this growth and characterization methodology. In particular, the role of electron-phonon coupling in the recent SrTiO₃-based superconductors and the magnetic behavior of isolated strongly spin-orbit coupled SrIrO₃ layers will be discussed. We will conclude this talk with a discussion of the promising future applications for this class of materials, with an emphasis on topological phenomena and quantum information science.

Title: Quantum quench and nonequilibrium dynamics in lattice-confined spinor Bose-Einstein condensates
Yingmei Liu, Oklahoma State University

Friday, November 6th, 2020
12:00-1:00pm (Zoom link will be announced)

Bose-Einstein condensates (BECs) are ultra-cold gases, in which all atoms have a single collective wavefunction for their spatial degrees of freedom. With an additional spin degree of freedom, spinor BECs constitute a collective quantum system offering an unprecedented degree of control over such parameters as spin, density, temperature, and the dimensionality of the system. Spinor BECs have thus been considered as good quantum simulators for verifying and optimizing condensed matter models. In this talk, I will discuss a novel quantum phase transition realized in our antiferromagnetic spinor BEC system. I will also present our experimental study on nonequilibrium dynamics of a spinor BEC after it is quenched across a superfluid to Mott insulator phase transition in cubic lattices. Intricate few-body dynamics consisting of spin-mixing oscillations at multiple frequencies are observed after distinct quantum quench sequences. We confirm these observed spin-mixing spectra can be utilized to reveal atom number distributions of an inhomogeneous system, to study transitions from two-body to many-body spin dynamics, and to precisely measure two key parameters determining the spinor physics. 

Title: Impact of nonparabolic electronic band structure on the optical and transport properties of photovoltaic materials

Lucy Whalley, Northumbria University

Friday, November 13th, 2020
12:00-1:00pm (Zoom link will be announced)

Abstract: The effective mass approximation (EMA) models the response to an external perturbation of an electron in a periodic potential as the response of a free electron with a renormalized mass. For semiconductors used in photovoltaic devices, the EMA allows calculation of important material properties from first-principles calculations, including optical properties (e.g., exciton binding energies), defect properties (e.g., donor and acceptor levels), and transport properties (e.g., polaron radii and carrier mobilities). The conduction and valence bands of semiconductors are commonly approximated as parabolic around their extrema, which gives a simple theoretical description but ignores the complexity of real materials. In this talk I will assess the impact of band nonparabolicity on the optical and transport properties of four thin-film photovoltaic materials (CdTe, GaAs, Cu₂ZnSnS₄ , CH₃NH₃PbI₃) at temperatures and carrier densities relevant for real-world applications.

Title: Fundamental Limitations of Classical, Linear, Time-Invariant Antennas

Jessica Ruyle, University of Oklahoma

Friday, November 20th, 2020
12:00-1:00pm (Zoom link will be announced)

Abstract: Any wireless system, from communication systems to radar, must have an antenna to transduce energy into an electromagnetic wave. This presentation will discuss the fundamental limitations of classical, linear, time-invariant (LTI) antennas. I will show the findings of antenna literature over the past 70 years, deriving bounds on performance of LTI antennas in directionality, efficiency, and bandwidth. These performance bounds translate into limitations on system performance. Antenna researchers are currently investigating fundamentally different structures to act as electromagnetic wave transducers to overcome these classical bounds on performance. 

Title: Quantum archaeology: How much time does an atom spend in a region it’s not allowed to enter, and how much time do photons spend inside atoms that don’t absorb them?

Aephraim M. Steinberg, University of Toronto

Friday, December 11th, 2020
12:00-1:00pm (Zoom link will be announced)

Abstract: One of the most famous tidbits of received wisdom about quantum mechanics is that “you can’t ask” which path a photon took in an interferometer once it reaches the screen, or in general, that only questions about the specific things you finally measure are well-posed at all.  Much work over the past decades has aimed to chip away at this blanket renunciation, and investigate “quantum retrodiction.”  Particularly in light of modern experiments in which we can trap and control individual quantum systems for an extended time, and quantum information protocols which rely on “postselection,” these become more and more timely issues.

All the same, the first experiment I wish to tell you about addresses a century-old controversy: that of the tunneling time.  Since the 1930s, and more heatedly since the 1980s, the question of how long a particle spends in a classically forbidden region on those occasions when quantum uncertainty permits it to appear on the far side has been a subject of debate.  Using Bose-condensed Rubidium atoms cooled down below a billionth of a degree above absolute zero, we have now measured just how long they spend inside an optical beam which acts as a “tunnel barrier” for them.  I will describe these ongoing experiments, as well as proposals we are now refining to study exactly how long it would take to “collapse” an atom to be in the barrier.

I will also say a few words about a more recent experiment, which looks back at the common picture that when light slows down in glass, or a cloud of atoms, it is because the photons “get virtually absorbed” before being sent back along their way.  It turns out that although it is possible to measure “the average time a photon spends as an atomic excitation,” there seems to be no prior work which directly addresses this, especially in the resonant situation.  We carry out an experiment that lets us distinguish between the time spent by transmitted photons and by photons which are eventually absorbed, asking the question “how much time are atoms caused to spend in the excited state by photons which are not absorbed?”

Optical Probe of Coherent States in Multi-Functional Materials

Giti Khodaparast, Virginia Tech 

Friday, January 17, 2020
11:30am-12:30pm
Lin Hall, 105

Intense laser pulses can generate carriers, spins, phonons, and magnons far from equilibrium states.  Information about the dynamical behavior of these nonequilibrium states can be elucidated by:  1)the electronic structure, 2)carrier scattering and relaxation mechanisms, including carrier-phonon and carrier-carrier scattering, 3)spin and magnetization dynamics, and 4)dynamical many-body interactions. For example,coherent acoustic phonons which are ultrasonic strain pulses can result in a broad optical spectrum from GHz up to THz.  The possibility of manipulating Coherent Phonons (CP) could lead to develop new techniques such acoustic imaging as well as better understanding and control of electronic and optical properties in devices.  Exploring the interaction of CP with carriers, magnetic impurities, and photons can open new prospective of phononics on nanoscale. For example, the manipulation of spins in semiconductors without the application of magnetic fields opens the door to the next generation of devices, where the electronic computation and magnetic memory can be performed on the same chip.Inthis talk, I will present several time resolved studies including CP generation and control in multifunctional materials such as ferromagnetic semiconductors and mutliferroics. 

Title TBA
Prof. Yi Zho, Shanghai Tech University, China

Friday, February 11, 
1:15-2:15pm
Lin Hall, 105

Cancelled due to travel complications.  

This seminar will be rescheduled at a later date if possible.

APS Conference Talks from Cancelled March Meeting
Various speakers

Friday, March 6, 2020, 
11:30-1:30pm
Lin Hall, 105

Experiment: 

• 11:30:  F63.00008 : Hot Carrier Dynamics in Bulk and 2D Perovskites, Shashi Sourabh
• 11:42:  J21.00005 : Valley Photovoltaics: Experimental Evidence for a Practical Route towards the Realization of the Hot Carrier Solar Cell, Kyle R Dorman
• 11:54:  J21.00008 : A low-temperature-low-intensity study of flexible CIGS solar cells, Hadi Afshari
• 12:06:  J21.00011 : Hot carrier dynamics in Quantum Well Solar Cells (Thermal Photon Gain), Brandon Durant

12:18:  Break

Theory:

• 12:30:  C71.00017 : Topological Effects in Knotted Arrays of One-Dimensional Quantum Rings, Colin Riggert
• 12:42:  P53.00007 : Applying Machine Learning to Thermal Conductance, Alexander Kerr
• 12:54:  S56.00013 : Interactions in nodal-line semimetals with quadratic band touching, Geo Jose
• 1:06:  R15.00003 : Fluid Flow Mechanisms in Shale Organic Nanopores, Felipe Perez Valencia (Petroleum & Geological Engin)

Title Applying quantum Zeno effect to noise sensing and geometrical phase detection
Dr. Hoang Van Do, University of Oklahoma

Friday, March 13, 2020 
11:30am-12:30pm
Lin Hall, 105

Abstract: Dynamical decoupling methods have been introduced to protect a quantum dynamical evolution from decoherence and to infer specific features of the noise spectrum originating from the environment. By measuring the quantum system frequently enough, the system is placed into the so-called quantum Zeno regime. This regime is demonstrated in a Bose-Einstein condensate (BEC) of rubidium-87 atoms on a chip at the 

European Laboratory for Non-Linear Spectroscopy in University of Florence. 

This regime not only provides a robust method for quantum control of populations but also maintains the coherence of the system, the geometric and dynamical phases acquired during evolution in the presence of measurement back-action are evaluated. Furthermore, when a state evolves through a closed loop on the Bloch sphere, it gains a geometric phase factor precisely corresponding to half the solid angle of the closed loop as shown in Phys. Rev. Research 1, 033028 (https://doi.org/10.1103/PhysRevResearch.1.033028). 

Dynamical decoupling methods can be also exploited in sensing technologies. Noise spectroscopy can be carried out by applying a sequence of projective measurements. This procedure induces the loss of atoms in the initial state, with a probability that presents maximal fluctuations when the measurement frequency is resonant with the noise frequency. The noise spectrum can be extracted with $80-90\%$ fidelity. This work is publised in New J. Phys. 21 (https://doi.org/10.1088/1367-2630/ab5740). 

This presentation will also report a collaboration with the Department of Computer Science of Seoul National University. Here, using reinforced--learning methods, we searched for different experimental schemes to produce high--dimensional tripartite entangled states of photons and to assemble inter--level couplings to fabricate quantum logic gates in trapped ions..  

Title:  Quantum quench and nonequilibrium dynamics in lattice-confined spinor Bose-Einstein condensates 

Yingmei Liu, Oklahoma State University

Tuesday, April 7, 2020
1:15pm-2:15pm
Lin Hall, 105

Bose-Einstein condensates (BECs) are ultra-cold gases, in which all atoms have a single collective wavefunction for their spatial degrees of freedom. With an additional spin degree of freedom, spinor BECs constitute a collective quantum system offering an unprecedented degree of control over such parameters as spin, density, temperature, and the dimensionality of the system. Spinor BECs have thus been considered as good quantum simulators for verifying and optimizing condensed matter models. In this talk, I will discuss a novel quantum phase transition realized in our antiferromagnetic spinor BEC system. I will also present our experimental study on nonequilibrium dynamics of a spinor BEC after it is quenched across a superfluid to Mott insulator phase transition in cubic lattices. Intricate few-body dynamics consisting of spin-mixing oscillations at multiple frequencies are observed after distinct quantum quench sequences. We confirm these observed spin-mixing spectra can be utilized to reveal atom number distributions of an inhomogeneous system, to study transitions from two-body to many-body spin dynamics, and to precisely measure two key parameters determining the spinor physics. 

OK-PVRI symposium plenary talk

5:00pm, Nielsen Hall 170

This talk will be the plenary presentation for the OK Photovoltaic Research Institute symposium.  More details will be announced when the schedule is made final.

Title: TBD
Aephraim M. Steinberg, University of Toronto

Tuesday, April 14, 2020
1:15pm-2:15pm
Lin Hall, 105

Title: Quantum sensors and their networks as exotic field telescopes in multi-messenger astronomy
Andrei Derevianko,  University of Nevada, Reno

Tuesday, April 21, 2020
1:15pm-2:15pm
Lin Hall, 105

In my talk, I will focus on  exotic bosonic fields potentially sourced by powerful astrophysical events, such as binary neutron star and binary black hole  mergers. Because such hypothetical fields are predicted to feebly interact with standard model particles and fields,  we propose to employ precision quantum sensors to detect potential bursts of such exotic fields. We show that to unambiguously correlate such bursts with gravitational wave triggers, the fields must be ultralight and ultrarelativistic. Moreover, networks of precision sensors are required to resolve the progenitor position in the sky thereby establishing a crucial coincidence with the more conventional, e.g., electromagnetic or gravitational wave, observations of the source.  We show that within certain models,  atomic clocks and magnetometers can be sensitive to intense bursts of exotic fields  from astrophysical sources within the reach of current gravitational wave observatories. This opens an intriguing possibility for a novel, exotic physics, modality in multi-messenger astronomy.

Mid-IR to Thz nanophotonics: materials-based approaches to quantum photonics
Joshua Caldwell, Vanderbilt University

Friday, August 23, 2019
11:30am-12:30pm
Lin Hall, 105

The field of nanophotonics is based on the ability to confine light to sub-diffractional dimensions. Up until recently, research in this field has been primarily focused on the use of plasmonic metals. However, the high optical losses inherent in such metal-based materials has led to an ever-expanding effort to identify, low-loss alternative materials capable of supporting sub-diffractional confinement. One highly promising alternative is to implement polar dielectric crystals, whereby sub-diffraction confinement of light can be achieved through the stimulation of surface phonon polaritons within an all-dielectric, and thus low loss material system. Due to the wide array of high quality crystalline species and varied crystal structures, a wealth of unanticipated optical properties have recently been reported. Specifically, the recent demonstration of hyperbolic behavior within natural polar crystals provides exciting opportunities in on-chip, sub-diffractional refractive optics and a dramatically expanded density of states that can provide avenues for strong light matter interactions and control of emission rates. This talk will discuss recent advancements from our group including the realization of localized phonon polariton modes, the observation and exploitation of the natural hyperbolic behaviors in strongly anisotropic crystals, the detection of dark hyperbolic modes and polaritonic ultrastrong coupling phenomena.

Infrared Optical Circuitry for Quantum Technologies
 Joseph Tischler, Naval Research Lab

Wednesday, September 11, 2019
1:15-2:15pm
Lin Hall, 105

Analogously to plasmon polaritons, phonon polaritons in ionic crystals provide unparalleled optical confinement and therefore high local field intensity. Because phonon lifetimes are several orders of magnitude longer than lifetimes of photoexcited free carriers in metals, phonon polariton losses are significantly smaller resulting in sharp resonances that allow observation of physical effects otherwise obscured by the lack of spectral resolution. Also, the symmetry of the ionic crystal allows the observation of surface phonon polaritons and volume phonon polaritons. While isotropic crystals result in purely metallic spectral bands and therefore surface phonon polaritons, anisotropic crystal can generate hyperbolic spectral bands and therefore volume phonon polaritons. In this work we present new physics of nanostructured ionic crystals that illustrate our current understanding of both volume and surface phonon polaritons. Furthermore, I will show some of our most recent work and ideas towards the exploitation of surface phonon polaritons to create optical circuitry based on collective behavior of surface phonon polariton molecules and/or solids.

Cool quantum optics with hot atoms
Irina Novikova, College of William and Mary 

Friday, September 20, 2019
11:30am-12:30pm
Lin Hall, 105

Efficient and reliable quantum communication will require the control of the quantum state of both photons and atoms. In this talk I will discuss a possible realization of strong coupling between quantum optical field and collective spin excitation in atomic vapor via electromagnetically induced transparency, as well as possible applications of the effect for precision metrology, generation of non-classical light and quantum imaging.

Towards the production and braiding of anyons with Rydberg Atoms in Optical Cavities
Eric Mueller, Cornell University 

Tuesday, September 24, 2019
1:15pm-2:15pm
Lin Hall, 105

Researchers are trying to find ways of engineering states of matter with interesting (and hopefully useful) entanglement properties.  I will discuss ways in which atoms in optical cavities can be used to achieve this goal.  In particular, after describing the big-picture, and giving some background information about the properties of atoms and optical cavities, I will present a situation where we predict that light will behave like a highly unusual quantum fluid, similar to the one formed by electrons in the fractional quantum Hall effect.  This fluid has excitations which act like particles which are neither bosons nor fermions.  I will explain how these anyonic statistics can be directly probed in an experiment.

Excitations and dynamics in inversion symmetry-broken phases
Jonathan Spanier, Drexel University

Friday, September 27, 2019
11:30am-12:30pm
Lin Hall, 105

Emergent phenomena in solids, whether they involve lattice, charge, spin, orbital, or other degrees of freedom, are attractive for creating, stabilizing and/or controlling novel states of matter.  New paradigms based on these phenomena are attractive candidates for capturing, converting, and carrying energy more efficiently.  I will discuss two intriguing electromagnetic wave-matter interaction phenomena that can emerge in non-centrosymmetric solids. The first involves visible-light generation of two types of photovoltaic currents, one of which transforms, remarkably, a band insulator into a high-mobility conductor.  In the second, we reimagine the energy landscape associated with a two-dimensional crystal defect that has traditionally been viewed as an impediment to the flow of radio-frequency microwave energy.  Under special conditions a resonant behavior emerges, enabling the material to exhibit dielectric properties that can exceed intrinsic limits.

Physics of the hybrid perovskite semiconductors
Alexander Zhakhidov, Texas University San Marcos

Friday, October 04, 2019
11:30am-12:30pm
Lin Hall, 105

Organic lead halide hybrid perovskites (HPs) is a novel promising class of materials for the low-cost printed solar cells (record power conversion efficiency - 23.7%), photodetectors, LEDs, sensors and other optoelectronic devices. Yet, the nature of light-matter interaction in HPs is still debated. Benchmark CH3NH3PbI3 perovskite is reported to have a structure with inversion symmetry. Yet, Bulk Photovoltaic Effect (BPVE) [1] and Second Harmonic Generation (SHG)[2] non-linear optical effects recently reported for this material require the inversion symmetry breaking. 

In our recent work we presented the Density Functional Theory (DFT) with +U Hubbard correction computational model that predicts the existence of polarons in HPs.[3] We argue that breaking of bulk inversion symmetry in these experiments can be caused by light-induced polarons, which lead to the collective distortion of the crystal lattice. In fact, the presence or absence of polarons in the MAPI films may explain the controversial reports on MAPI polarity. The reported effects may enable third generation perovskite solar cells with efficiency that exceed the Shockley–Queisser limit. Our observations also open new venues for perovskite spintronics and tunable THz sources. 

[1]. P.A. Obraztsov, et al., Comm. Physics 1, 14 (2018). 

[2]. A.A. Popkova, et al., OSA Technical Digest JW3A.49 (2018). [3]. E. Welch, et al., AIP Advances 6, 125037 (2016).

Rydberg physics in the single and few atom regime

Mark Saffman, University of Wisconsin 

Friday, November 15, 2019
11:30am-12:30pm
Lin Hall, 105

Rydberg interactions have emerged as a leading approach for implementing quantum computation and simulation with atomic qubits. The Rydberg blockade mechanism is the underlying effect leading to entanglement, with the potential for fidelity that is high enough to reach thresholds for quantum error correction. 

I will go “under the hood” in a neutral atom quantum computer and present approaches for achieving long coherence times and high fidelity entanglement using optimized pulse sequences. Fully scalable quantum computation will require error correction, which brings with it additional experimental requirements including crosstalk free qubit measurements. I will show how interspecies Rydberg interactions can be used to solve this challenge.      

Machine-Learning-Assisted Photonics: From Optimized Design to Quantum Measurements 

Alexandra Boltasseva, School of Electrical & Computer Engineering and Birck Nanotechnology Center, Purdue University

Monday, November 18, 2019
3:30pm-4:30pm
Nielsen Hall, 170

Emerging photonic concepts such as optical metamaterials, metasurfaces, novel lasers, single-photon sources and other quantum photonic devices together with novel optical material platforms promise to bring revolutionary advances to information processing and storage, communication systems, energy conversion, imaging, sensing and quantum information technology. In pursuit of the next generation of photonic technologies, machine learning approaches have emerged as a powerful tool to discover unconventional optical designs and even uncover new optical phenomena. In this talk, various photonic design approaches as well as emerging material platforms will be discussed showcasting machine-learning-assistedtopology optimization for efficient thermophotovoltaic metasurface designs as well as machine-learning enabled quantum optical measurements. The next steps on merging  photonic optimization with artificial-intelligence-assisted algorithms and materials properties for designing advanced photonic components will be outlined.

Molecular Beam Epitaxy of Mixed Arsenide-Antimonide Alloys for Optoelectronic Applications 

Stephanie Tomasulo, Naval Research Laboratory

Friday, November 22, 2019
11:30am-12:30pm
Lin Hall, 105

Mixed arsenide-antimonide (AsSb) materials have many potential applications including photovoltaics and infrared detection as they possess direct bandgaps (E_g) ranging from ~0.5 eV to ~1.8 eV.  However, synthesis of these materials is fairly immature and challenging.  In this presentation, we will explore the molecular beam epitaxy (MBE) of ~1.6 eV InAlAsSb lattice-matched to InP and ~0.04 eV metamorphic InAsSb on GaSb covering both ends of this E_grange.      

As the widest-E_g III-V material lattice-matched to InP, a high-efficiency, wide-E_g InAlAsSb solar cell would be beneficial toward maximizing efficiency of an all-lattice-matched triple-junction solar cell.  However, both the immaturity and mixed group-V nature of this alloy pose significant challenges, requiring in depth investigation. Initial attempts at MBE of InAlAsSb resulted in anomalously low photoluminescence emission energies, compared with energies extracted from variable angle spectroscopic ellipsometry. To further investigate the cause of this discrepancy, we performed a systematic study of the substrate temperature and V/III of In_0.26Al_0.74As_0.88Sb_0.22 (expected E_g=1.64 eV) and will report the results in this presentation.  

At the other end of the E_g range, we have metamorphic InAsSb, which possesses the lowest E_g of all the conventional III-V materials, making it attractive for mid-to-long wavelength IR applications.  However, since the composition possessing the lowest E_g is not lattice-matched to existing substrates, compositional graded buffers are required to slowly grade the lattice-constant from that of the substrate to that of the desired composition in order to maintain a low defect density.  Here we will present metamorphic step-graded InAs_1-xSb_x buffers on GaSb, enabling the study of Sb incorporation as a function of growth conditions over a range of x (~0.1-0.6). We also present investigation of the optimal growth conditions and effect of growth conditions on dislocation dynamics in this low-E_g material system.    

Spin-helical particles: an enabling platform for quantum matter and quantum technologies

Yong Chen, Purdue University

Thursday, December 5, 2019
1:30pm-2:30pm
Lin Hall, 105

Spin is one of the most fundamental quantum properties of particles.  In this talk I will describe our experimental studies of “spin-helical” particles (analogous to neutrinos with spin locked to the momentum, but for electrons and atoms) as a powerful platform to realize novel quantum matter and enable new applications in quantum technologies --- ranging from quantum information/simulation to, quantum chemistry/energy.    For example the spin-helical electrons on the surface of “topological insulators” (TI) enabled observation of a “topological spin battery” [1] that opens a unique possibility to electrically induce and readout a nuclear and electronic spin polarization. Observations of unusual behaviors in Josephson junctions and SQUIDs made of our TIs [2] that may be relevant for the study of “topological superconductor” and “majorana fermions” with promise for “topologically protected” quantum computing.   As another example, spin-helical bosons in a Bose-Einstein condensate (BEC) of laser-cooled atoms with “synthetic” spin orbit coupling and gauge fields allow us to dynamically control the Hamiltonian and perform various quantum transport, interferometry, chemistry, and even “collider” experiments.  We demonstrate a new “interferometric” approach for quantum control of chemical reactions by preparing reactants in spin superpositions [3]. The system could also be used as a quantum simulator to study phenomena ranging from spin decoherence in interacting systems [4] to novel quantum matter in extra “synthetic” dimensions or curved spaces not easily realized in electronic materials [5].   Time permitting, I may briefly discuss other research programs in my group and Purdue Quantum Science and Engineering Institute (PQSEI), ranging from quantum materials to quantum sensing. 

Refs: [1] J. Tian et al., “On the understanding of current-induced spin polarization of three-dimensional topological insulators”, Nature Comm. 10, 1461 (2019);

[2] M.Kayyalha et al., "Highly skewed current-phase relation in superconductor-topological insulator-superconductor Josephson junctions", arXiv:1812.00499;

[3] D.Blasing et al. "Observation of Quantum Interference and Coherent Control in a Photo-Chemical Reaction", PRL 121, 073202 (2018);

[4] C. Li et al."Spin Current Generation and Relaxation in a Quenched Spin-Orbit Coupled Bose-Einstein Condensate", Nature Comm. 10, 375 (2019);

[5] C.Li et al., "A Bose-Einstein Condensate on a Synthetic Hall Cylinder", arXiv:1809.02122

From Quantum Physics to Quantum Chemistry and Quantum Biology
Vladislav V. Yakovlev, Texas A&M University 

Friday, December 13, 2019
11:30am-12:30pm
Lin Hall, 105

Quantum mechanics provides the most accurate description of the world around us. Quantum effects play important role in developing the next generation of technologies, such as quantum computers and quantum communication. Quantum control ideas, which we developed in early 90’s [1], are now becoming reality and are being implemented for different practical applications.  My current research interests are revolving around imaging and sensing. I am particularly intrigued with precise measurements using quantum properties of molecular systems and quantum states of light which can provide new information with improved sensitivity and specificity. In my presentation I will provide some historical introduction and, after summarizing some of my prior and current work, will attempt to sketch some broader applications of quantum optical imaging and sensing.

[1] B. Kohler, et al "Controlling the future of matter," Accounts of Chemical Research 28, 133-140 (1995).