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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.

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 2019

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

Friday, August 23, 2019
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
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
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
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
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
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
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
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
Lin Hall, 105


Mixed arsenide-antimonide (AsSb) materials have many potential applications including photovoltaics and infrared detection as they possess direct bandgaps (Eg) 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 Egrange.      

As the widest-Eg III-V material lattice-matched to InP, a high-efficiency, wide-Eg 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 In0.26Al0.74As0.88Sb0.22 (expected Eg=1.64 eV) and will report the results in this presentation.  

At the other end of the Eg range, we have metamorphic InAsSb, which possesses the lowest Eg of all the conventional III-V materials, making it attractive for mid-to-long wavelength IR applications.  However, since the composition possessing the lowest Eg 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 InAs1-xSbx 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-Eg 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
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
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).

Spring 2020

Optical Probe of Coherent States in Multi-Functional Materials

Giti Khodaparast, Virginia Tech 

Friday, January 17, 2020
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, 
Lin Hall, 105

Abstract TBA