Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L02: Interacting Ultracold Gases, Light-Matter Coupling, and Cavities |
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Sponsoring Units: DAMOP Chair: Michael Feig, Honeywell Intl Room: 105 |
Wednesday, March 4, 2020 8:00AM - 8:12AM |
L02.00001: Three-color fermions under local and next-neighbor interactions Arturo Pérez, Roberto Franco Pe?aloza, Jereson Silva Valencia Graphene, Bechgaard salts, polymers and systems of adatoms on semiconductor surfaces can be described by an extended SU(2) Fermi-Hubbard model, which has a rich phase diagram that has been studied for decades. Ultracold atom setups have allowed testing and extending many ideas and concepts of condensed matter. Confining alkaline-earth-metal atoms, which have several hyperfine states allow to obtain SU(N>2) Fermi-Hubbard systems experimentally. |
Wednesday, March 4, 2020 8:12AM - 8:24AM |
L02.00002: Interaction-induced long-time tail of a nonlinear ac absorption in a localized system: a relay-race mechanism Mikhail Raikh, Rajesh Malla
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Wednesday, March 4, 2020 8:24AM - 8:36AM |
L02.00003: Unidirectional flow of solitons with nonlinearity management Majed Alotaibi, S. M. Al-Marzoug, H. Bahlouli, U. Al Khawaja Unidirectional flow of solitons is obtained with a localized modulation of the nonlinearity strength. The modulation takes the shape of an asymmetric double well with a slight difference between the potential depths. The results were established using numerical computations and then verified qualitatively using a variational approach. Our results suggest that the most important physics at the origin of the unidirectional flow is the excitation of the breathing modes in the scattering region. Simplified variational equations of motion suggested that the phenomenon can be observed if the soliton is scattered by a generic asymmetric effective double potential well. |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L02.00004: Cooperative Light Emission in the Presence of Strong Inhomogeneous Broadening Chen Sun, Vladimir Y Chernyak, Andrei Piryatinski, Nikolai Sinitsyn We study photon emission by an ensemble of two-level systems, with strong inhomogeneous broadening and coupled to a cavity mode whose frequency has linear time-dependence. The analysis shows that, regardless the distribution of energy level splittings, a sharp phase transition occurs between the weak and strong cooperative emission phases near a critical photonic frequency sweeping rate. The associated scaling exponent is determined. We suggest that this phase transition can be observed in an ensemble of negatively charged NV centers in diamond interacting with a microwave half-wavelength cavity mode even in the regime of weak coupling and at strong disorder of two-level splittings. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L02.00005: "Signal Energy" of an Excited Dipolar Bose Gas driven by an Oscillating Dimple Asaad R Sakhel, Roger Raji Sakhel It is known that dipolar Bose-Einstein condensates (DBECs) display rich and fascinating features that are not observable in nonpolar BECs (Lahaye et al., Rep. Prog. Phys. 72, 126401 (2009)). As such, the present examination studies the dynamics of a DBEC, being motivated by the work of Sabari and Kumar (Eur. Phys. J. D 72, 48 (2018)) who examined the effect of an oscillating obstacle in a DBEC. We thus examine the "signal energy" of a trapped DBEC that is driven by an oscillating dimple potential. For this purpose we numerically solve the time-dependent Gross-Pitaevskii equation. The signal energy is related to the energy spectral density. It is demonstrated that the signal energy displays parametric resonances (PRs) at specific values of the dipole-dipole interaction parameter that can be controlled via the trapping geometry. The spacings between these values have been found to reveal information about the energy level structure of the external trap. The dynamics of the harmonic-oscillator (HO)-states occupancy obtainable from the modal coefficients Cn(t) arising in the decomposition of the wave function Ψ(x;t) = ∑n=0 Cn(t) φn (x), where φn (x) is the usual HO function, as well as the phase-mismatch between C0(t) and C1(t) have been found to display challenging features at PR. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L02.00006: Contour-time approach to the 2D disordered Bose-Hubbard model in the strong coupling regime. Matthew Fitzpatrick, Ali Mokhtari-Jazi, Malcolm P Kennett We develop a strong-coupling approach for calculating spatio-temporal correlations in the disordered Bose-Hubbard model. We consider systems that are prepared in highly-excited out-of-equilibrium density patterns and derive equations of motion for the disorder-averaged single-particle Green's function, allowing us to study the relaxation dynamics. We discuss how our formalism can be applied to the study of Bose glass and possibly many-body localized states in the context of recent cold experiments. |
Wednesday, March 4, 2020 9:12AM - 9:24AM |
L02.00007: Study of Low Energy Excitations of Cold Atomic Fermi Systems using Quantum Monte Carlo Methods Kaelyn Dauer, Ettore Vitali, Annette Lopez, Patrick Kelly The calculation of dynamical properties of quantum many-body theories is a big challenge from both the theoretical and computational point of view. Quantum Monte Carlo methods are considered to be some of the most accurate apporaches for unravelling physical mechanisms in systems where correlations are so strong that simple approaches are doomed to fail. Most of the success of Quantum Monte Carlo techniques involve static properties of physical systems, like phase diagrams and density correlations. The extension to dynamical quantities, like the spectrum of density fluctuations or the spectral function is still a major challenge, despite some important recent successes. Cold atomic Fermi systems are unique due to the unprecedented experimental control that can be achieved and due to the flexibility of hamiltonians that can be engineered. This makes them a unique test ground for correlated methodologies like Quantum Monte Carlo. In this presentation we will review important recent advances in the calculations, and we will present new results about the spectrum of density fluctuations and spectral functions of Fermi gases. |
Wednesday, March 4, 2020 9:24AM - 9:36AM |
L02.00008: Broadband sensitivity improvement via coherent quantum feedback with PT symmetry Xiang Li, Rana Adhikari, Vaishali Adya, Yanbei Chen, Yifan Chen, Maxim Goryachev, Yiqiu Ma, Jing Shu, Michael Tobar, Robert L Ward, Chunnong Zhao A conventional resonant detector is subject to a trade-off between bandwidth and peak sensitivity. This limitation can be traced back to the Quantum Cramer Rao Bound and the coherent state of the conventional resonator. The trade-off can be broken by injecting non-classical states (e.g., squeezed vacuum), but it often has stringent requirements on optical losses. Anomalous dispersion due to an unstable quantum system has been shown to be able to improve the bandwidth-sensitivity product by signal amplification and thus suffer less from losses. But stabilizing the system may cause technical complications and conceptual issues. Here we propose a simple stable quantum amplifier enabled by two-mode non-degenerate parametric amplification. We demonstrate that coherent broadband signal amplification can be achieved without incurring instability. As the amplifier operates at the threshold, one mode of the amplifier forms a PT-symmetric system of the original detector mode, while the other mode collects the signal and transfer it to the readout. We will discuss how to apply this strategy to gravitational-wave detectors. |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L02.00009: Interacting Bose-Bose mixtures at finite temperature Arko Roy, Miki Ota, Alessio Recati, Franco Dalfovo We examine the role of thermal fluctuations in 2D uniform binary condensate mixtures of dilute atomic gases. In particular, we use the Stochastic Projected Gross-Pitaevskii formalism to probe the impact of non-condensate atoms to the phenomenon of phase-separation in two-component Bose-Einstein condensates. We demonstrate that, in comparison to zero temperature, there is a suppression in the phase-separation of the binary condensates at non-zero temperature. We also show that a mixed phase gives rise to a fully separated one at finite temperature. Finally, these phases are characterized by measuring the speed of sound at finite temperature. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L02.00010: Superradiant Peierls transition in a multi-mode optical cavity Colin Rylands, Benjamin L Lev, Jonathan Keeling, Victor Galitski The strong matter-light coupling attainable in optical cavities has been employed with remarkable success to study quantum systems. It has facilitated the realization of many exciting phenomena from superradiance and self organization of matter to exciton-polaritons condensates. We consider such a system in which a one dimensional interacting Bose gas is loaded into a multi-mode optical cavity and subject to a pump field. Focusing on the steady state properties of the system we find that for sufficiently strong repulsive interactions a superradiant transition takes place which is accompanied by a metal insulator transition in the atomic system. In the limit of infinite repulsion this is attributable to the Peierls instability. Away from this special point we show that this still occurs however the nature of the transition changes and upon further reducing the interaction strength the system undergoes a transition to a gapless normal state. |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L02.00011: Microscopic Origins of the Hess-Fairbank Effect and its Consistency with the Second Law of Thermodynamics Anthony J Leggett, Douglas Packard The history of applying kinetic theory to help us understand superfluid and BEC phenomena is a long and storied one, going back to the work of Landau and Khalatnikov [1]. Further developments were made using quantum field theoretic [2] and quantum optical methods [3]. We use these methods to study the nonequilibrium physics of Bose condensation and superfluid formation in a rotating quantum fluid. In particular, we examine the quantization of angular velocity observed at low rotational speeds, i.e. the Hess-Fairbank effect. We present results relating the transfer of atoms into a condensate or superfluid mode (at rest in the lab frame) to the overall generation of entropy, taking the rotating container of the fluid itself into account. Finally, we attempt to relate these results to the phenomenon of flux expulsion from a bulk superconductor, in light of recent critical papers on this topic [4]. |
Wednesday, March 4, 2020 10:12AM - 10:24AM |
L02.00012: Structure of chaotic eigenstates and their entanglement entropy Chaitanya Murthy, Mark Srednicki We consider a chaotic many-body system (i.e., one that satisfies the eigenstate thermalization hypothesis) that is split into two subsystems, with an interaction along their mutual boundary, and study the entanglement properties of an energy eigenstate with nonzero energy density. When the two subsystems have nearly equal volumes, we find a universal correction to the entanglement entropy that is proportional to the square root of the system’s heat capacity (or a sum of capacities, if there are conserved quantities in addition to energy). This phenomenon was first noted by Vidmar and Rigol in a specific system; our analysis shows that it is generic, and expresses it in terms of thermodynamic properties of the system. Our conclusions are based on a refined version of a model of a chaotic eigenstate originally due to Deutsch, and analyzed more recently by Lu and Grover. |
Wednesday, March 4, 2020 10:24AM - 10:36AM |
L02.00013: Mixed spectra and partially extended states in a two-dimensional quasiperiodic model Attila Szabo, Ulrich Schneider We introduce a two-dimensional generalisation of the quasiperiodic Aubry-André model. Even though this model exhibits the same duality relation as the one-dimensional version, its localisation properties are found to be substantially more complex. In particular, partially extended single-particle states appear for arbitrarily strong quasiperiodic modulation. They are concentrated on a network of low-disorder lattice lines, while the rest of the lattice hosts localised states. This spatial separation protects the localised states from delocalisation, so no mobility edge emerges in the spectrum; instead, localised and partially extended states are interspersed, giving rise to an unusual type of mixed spectrum. In the absence of interactions, this mixed spectrum also gives rise to complex dynamics, such as ballistic transport across the low-disorder lines, while the rest of the system remains localised. This behaviour is robust against disorder and other weak perturbations. Our model is thus directly amenable to experimental studies and promises fascinating many-body localisation properties. |
Wednesday, March 4, 2020 10:36AM - 10:48AM |
L02.00014: Efimov physics in the presence of a Fermi sea Mingyuan Sun I will introduce the Efimov correlation in atomic system of two heavy bosons (133Cs) immersed in a bath of light fermions (6Li). Using the Born-Oppenheimer approximation, we identify two different regimes, depending on the Fermi momentum of light fermions ( kF ) and the boson-fermion scattering length as(< 0), where the presence of underlying Fermi sea plays distinct roles in the Efimov-type binding of bosons. Namely, in the regime kF |as| < 1 ( kF |as| > 1 ), the Fermi sea induces an attractive (repulsive) effective interaction between bosons and thus favors (disfavors) the formation of bound state, which can be seen as the Efimov trimer dressed by the fermion cloud. Interestingly, this implies a non-monotonic behavior of these bound states as increasing the fermion density (or kF ). Moreover, we establish a generalized universal scaling law for the emergence/variation of such dressed Efimov bound states when incorporating a new scale ( kF ) brought by the Fermi sea. |
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