## Previous CQRT Seminars

The Atomic, Molecular and Optical (AMO) and Condensed Matter (CM) physics groups are hosting a joint seminar as part of the Center for Quantum Research and Technology (CQRT). This endowed seminar will bring in experts from across the country as well as across campus to discuss the latest in research advances in quantum science.

### Fall 2021 (virtual Zoom series)

**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 (LuFeO _{3})_{m}/(LuFe_{2}O_{4})_{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.

### Spring 2021 (Virtual Seminar Series)

**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 Ga _{2}O_{3} 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-Ga_{2}O_{3}) 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 Ga_{2}O_{3}. 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 Ga_{2}O_{3}.

**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.

Seminars meet in 105 Lin Hall and will usually be held on Tuesdays from 1:15-2:15pm. However, in order to accommodate the travel schedules of visitors, we may occasionally meet Fridays from 11:30am-12:30pm.

### Fall 2020 (Virtual Seminar Series)

**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].

- C-Y. Hsieh, et al., Rep. Prog. Phys.
**75**, 114501 (2012). - Blazej Jaworowski et al.,
**Nature**Scientific Reports 7, 5529 (2017). - 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.
- M. Korkusinski, et al., Nature Scientific Reports 4, 4903(2014).
- Fengjia Fan, et. al. Nature 544, 75 (2017).
- D.Guclu, et. al. ”Graphene Quantum Dots”, Springer-Verlag (2014).
- Y. Saleem, et. al., Journal of Physics: Condensed Matter 31 (30), 305503 (2019).
- L.Szulakowska, et al, Phys. Rev. B 2020 (submitted).
- T. Scrace, et al., Nature Nanotechnology 10, 603 (2015).
- 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 SrTiO_{3}-based superconductors and the magnetic behavior of isolated strongly spin-orbit coupled SrIrO_{3} 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, Cu_{2}ZnSnS_{4} , CH_{3}NH_{3}PbI_{3}) 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?”

### Spring 2020

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.

### Fall 2019

**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.

### Note special date, time and venue

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_{g}range.

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_{0.26}Al_{0.74}As_{0.88}Sb_{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-x}Sb_{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.

### Note special date, time and venue

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).

**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.