Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D02: Nonequilibrium Dynamics in Ultracold Matter 
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Sponsoring Units: DAMOP Chair: Christian Gross, MaxPlanckInstitute for Quantum Optics Room: 105 
Monday, March 2, 2020 2:30PM  2:42PM 
D02.00001: Quantum Cherenkov Transition in Bose Polaron Systems Kushal Seetharam, Yulia Shchadilova, Fabian Grusdt, Mikhail Zvonarev, Eugene Demler We study the behavior of a finitemomentum impurity immersed in a weakly interacting BoseEinstein condensate (BEC) of ultracold atoms near an interspecies Feshbach resonance. Using the timedependent variational approach and a nonGaussian transformation, we study both ground state properties and quench dynamics of the system after a sudden immersion of the impurity into the BEC. While in the subsonic regime dynamics corresponds to relaxation into the quasiparticle state, in the supersonic regime we observe rapid emission of Cherenkov phonons. This phenomenon manifests in several ways during realtime dynamics of the system and showcases a rich interplay between polaronic physics and Cherenkov physics. We see qualitatively different longtime behavior of average impurity speed and Loschimdt echo depending on the impurityboson interaction strength. Aspects of the discussed dynamical behavior can be probed in experimental protocols. 
Monday, March 2, 2020 2:42PM  2:54PM 
D02.00002: Tuning of Scattering Resonances by TimePeriodic Driving Christoph Dauer, Axel Pelster, Sebastian Eggert, Piotr Chudzinski Scattering by a shortrange interparticle potential with timeperiodic modulation is investigated with Floquet theory without assuming any high frequency approximations. For a harmonic drive it turns out that strong resonances occur, which allow versatile tuning of the swave scattering length and the resonance width by adjusting frequency and driving amplitude. Our approach leads to a simple description of the effect in terms of a generalized FanoAnderson model, which in turn identifies the physical origin and leads to an analytic quantitative description of the resonances. Results for general experimental situations of magnetic and optical driving using two coupled channels and including higher harmonics are discussed. 
Monday, March 2, 2020 2:54PM  3:06PM 
D02.00003: Quench dynamics of twocomponent dipolar Fermions in a Quasiperiodic potential bradraj pandey, Elbio Dagotto, swapan K. pati Motivated by the recent experiments in fermionic polar gases, we study the quenched 
Monday, March 2, 2020 3:06PM  3:18PM 
D02.00004: Enabling ultrastrongcoupling phenomena with singledrive JaynesCummings models Carlos Sánchez Muñoz, Anton Frisk Kockum, Adam Miranowicz, Franco M Nori We propose the effective simulation of lightmatter ultrastrongcoupling phenomena with strongcoupling systems. Recent theory and experiments have shown that the singleatom quantum Rabi model can be simulated by the JaynesCummings model with two additional classical drives. Here, we show that quantum nonlinear optical phenomena, relying on the counterrotating terms of the quantum Rabi model, can be implemented by the JaynesCummings and TavisCummings models with only a single classical drive. We analyze three examples (one atom exciting two photons, frequency conversion, and one photon exciting two atoms) and show that they could be demonstrated with several currently available experimental quantumoptics systems, including superconducting circuits and trapped ions. 
Monday, March 2, 2020 3:18PM  3:30PM 
D02.00005: Dynamics of the decay of dark solitons in superfluid Fermi gases Wout Van Alphen, Hiromitsu Takeuchi, Jacques Tempere Dark solitons are solitary matter waves which retain their shape while propagating at a constant velocity. They emerge in a wide variety of physical systems, including ultracold atomic gases. In superfluid Bose gases, dark solitons have been observed to decay into quantized vortices through the socalled snake instability mechanism. Recent experiments in superfluid Fermi gases have also interpreted soliton decay via this mechanism. However, using both numerical simulations and a perturbative analysis based on a lowenergy effective field theory, we show that there is a qualitative difference between soliton decay in the BEC and BCSregimes of superfluid Fermi gases. 
Monday, March 2, 2020 3:30PM  3:42PM 
D02.00006: Operator complexity of adiabatic gauge potential Mohit Pandey, Dries Sels, Pieter W. Claeys, Anatoli S Polkovnikov, David K Campbell Recently, there has been great interest in studying the growth rates of operator complexity and outoftimeorder correlators in manybody quantum systems. Here we characterize the complexity of the adiabatic gauge potential (AGP), which encodes the geometry of eigenstates when varying a control parameter in a Hamiltonian. For generic systems, the AGP is a highly nonlocal and entangled operator. We find that its Frobenius norm, which can be explicitly related to operator growth, shows remarkably different scaling with system size for integrable and nonintegrable systems: polynomial versus exponential. Using the length of Pauli string operator as a measure of the AGP complexity, we compute operator weight distributions and the Shannon entropy to better understand the norm's system size scaling. 
Monday, March 2, 2020 3:42PM  3:54PM 
D02.00007: Transport in a bosonic superfluid point contact Shun Uchino, JeanPhilippe Brantut

Monday, March 2, 2020 3:54PM  4:06PM 
D02.00008: Entanglement production by interaction quenches of quantum chaotic subsystems Jethin Pulikkottil Jacob, Arul Lakshminarayan, Shashi C. L. Srivastava, Arnd Bäcker, Steven Tomsovic The entanglement production in bipartite quantum systems is studied for initially unentangled product eigenstates of the subsystems, which are assumed to be quantum chaotic [1]. Based on a perturbative computation of the Schmidt eigenvalues of the reduced density matrix, explicit expressions for the timedependence of entanglement entropies, including the von Neumann entropy, are given. An appropriate rescaling of time and the entropies by their saturation values leads a universal curve, independent of the interaction. The extension to the nonperturbative regime is performed using a recursively embedded perturbation theory to produce the full transition and the saturation values. The analytical results are found to be in good agreement with numerical results for random matrix computations and a dynamical system given by a pair of coupled kicked rotors. 
Monday, March 2, 2020 4:06PM  4:18PM 
D02.00009: The entanglement membrane in deterministic systems Tianci Zhou, Adam Nahum In certain analyticallytractable quantum chaotic systems, the calculation of outoftimeorder correlation functions, entanglement entropies after a quench, and related dynamical observables, reduces to an effective statistical mechanics of an ‘entanglement membrane’ in spacetime. These tractable systems involve an average over random local unitaries defining the dynamical evolution. We show here how to make sense of this membrane in more realistic models, which do not involve an average over random unitaries. Our approach relies on introducing effective ‘pairing’ degrees of freedom in spacetime, inspired by the structure emerging in random unitary circuits. We also provide an efficient algorithm for determining the ‘line tension’ of the entanglement membrane in 1+1D models. 
Monday, March 2, 2020 4:18PM  4:30PM 
D02.00010: Nonequilibrium dualboson approach Feng Chen, Michael Galperin, Mikhail Katsnelson We develop nonequilibrium auxiliary quantum master equation dual boson method (auxDB), 
Monday, March 2, 2020 4:30PM  4:42PM 
D02.00011: Modeling Collective Emission in Cavities by Phase Space Trajectories Tao Li, Hsing Ta Chen, Abraham Nitzan, Joseph E Subotnik We model N electronic twolevel systems (TLSs) coupled to a multimode cavity by sampling independent trajectories in Wiger phase space with a MeyerMillerStockThoss (MMST) mapping Hamiltonian. We show that this approach can not only provide us an intuitive physical interpretation of quantum electrodynamics (i.e. sampling electronic and photonic zeropoint energies in phase space represents radiative selfinteraction and vacuum fluctuations respectively), but also correctly describe many intriguing collective emission phenomena, including spontaneous emission for an array of TLSs in the singly excited manifold, Dicke's superradiance and subradiance when all TLSs are excited, and even the quantum statistics for the delay time in superradiance. We also discuss possible further improvements of this approach. 
Monday, March 2, 2020 4:42PM  4:54PM 
D02.00012: The role of integrability in speeding up collective spin polarization. Tamiro Villazon, Pieter W Claeys, Anatoli S Polkovnikov, Anushya Chandran The central spin problem plays an important role in a variety of condensed matter systems, including quantum dots and nitrogen vacancy centers in diamond. We study an anisotropic central spin model with two classes of special eigenstates: bright and dark. We find these states to be robust against perturbations around two integrable points of the model. By driving of the central magnetic field, the structure of these eigenstates can be harnessed to access highly polarized manybody configurations. Using approximate shortcuts to adiabaticity, we develop a highly efficient and experimentally viable polarizing scheme. 
Monday, March 2, 2020 4:54PM  5:06PM 
D02.00013: Quantum Weak Measurement Backaction Control On A Strongly Interacting BEC Yueheng Shi, Stuart Szigeti, Arjendu Kishore Pattanayak The choice of weak measurement phase can affect the energy dynamics of a nonlinear quantum system. We report on progress towards controlling the measurement backaction on a strongly interacting Bose Einstein condensate (BEC) continuously monitored under phasecontrast imaging setup. We have derived the master equation using the fixed number state approximation. These have been reduced to a coupled set of differential equations of motions under Gaussian Approximation for the BEC. We use measurement phase dependent backaction in these equations for feedback control. We discuss potential applications and experimental realizations. 
Monday, March 2, 2020 5:06PM  5:18PM 
D02.00014: Unitary Subharmonic Response of Floquet Majorana Modes Oles Shtanko, Ramis Movassagh Detection and manipulation of Majorana fermions are essential for creating a topological quantum computer. To this end, we show that unpaired Majorana modes in Floquet systems can directly be visualized using the phenomenon of unitary subharmonic response. Namely, starting from highly nonequilibrium initial states, the unpaired Majorana modes exhibit boundary oscillations that have twice the driving period, are localized, and have up to exponentially long lifetimes with respect to the system's parameters. While the lifetime is still limited in translationally invariant systems, we show how disorder can be engineered to stabilize the subharmonic response of Majorana modes. We also suggest a viable implementation in modern multiqubit systems, such as superconducting circuits and atomic systems. 
Monday, March 2, 2020 5:18PM  5:30PM 
D02.00015: Real time dynamics of impurity and disorder scattering with interacting Fermion wave packets Sebastian Eggert, Kevin Jägering, Imke Schneider, Benjamin Nagler, Artur Widera Recent advances for ultracold gases allow the controlled scattering by disorder and localized impurities using moving interacting Fermion wave packets in a trap after a quick displacement in position. We analyze the damping and scattering behavior from large scale numerical tDMRG simulations in 1D as a function of interaction, displacement and disorder strength in a regime where a comparison with our experiments is possible. Attractive interactions make the wavepackets more susceptible for both single impurities and disorder scattering, which leads to a significant larger damping and quicker breakdown of the oscillations. Repulsive interactions have a much smaller effect, but overall a reduction of scattering can be observed. The corresponding experiments for 3D scattering show maximum stability and minimal damping near the unitary point. 
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