Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C13: Non-Equilibrium Physics with Ultracold Atoms IIFocus
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Sponsoring Units: DAMOP Chair: Fabian Grusdt, Harvard University Room: 272 |
Monday, March 13, 2017 2:30PM - 3:06PM |
C13.00001: Emergence of a Turbulent Cascade in a Quantum Gas Invited Speaker: Nir Navon The recent realisation of Bose-Einstein condensates in uniform traps [1] has opened interesting possibilities to study far-from-equilibrium phenomena with textbook systems [2]. In this talk, we will present a study where we drive a homogeneous Bose-Einstein condensate (BEC) out of equilibrium with an oscillating force that pumps energy into the system at the largest lengthscale [3]. In the limit of weak drives, the BEC's response is linear, well captured by its lowest-lying excitations. For stronger drives, a nonlinear response is apparent and we observe a gradual development of a cascade characterised by an isotropic power-law distribution in momentum space. We will report on our latest progress on the detailed characterisation of the steady-state turbulent state. [1] A. L. Gaunt et al., Phys. Rev. Lett. 110, 200406 (2013) [2] N. Navon et al., Science 347, 167 (2015) [3] N. Navon et al., Nature 539, 72 (2016) [Preview Abstract] |
Monday, March 13, 2017 3:06PM - 3:18PM |
C13.00002: Quantum Gases under inflation Cheng Li, Tin-Lun Ho Current technology is able to construct confining traps for quantum gases of the form of closed surfaces. By expanding these surfaces at a rate faster than speed of sound, the trapped gas can be "inflated". We shall discuss the key features of a quantum gas evolve under inflation, and how interaction effects manifest themselves in the inflation process. [Preview Abstract] |
Monday, March 13, 2017 3:18PM - 3:30PM |
C13.00003: Light-cone spreading of correlations after a quantum quench in the Bose-Hubbard model in 1 and 2 dimensions Matthew Fitzpatrick, Malcolm Kennett The quench dynamics of the Bose-Hubbard model (BHM) has received considerable attention in recent years. Theoretically, it has proven challenging to study spatio-temporal correlations in the BHM in dimensions higher than one. We use the Schwinger-Keldysh technique and a strong-coupling expansion to develop a two-particle irreducible formalism that allows the study of spatio-temporal correlations in both the superfluid (SF) and Mott-insulating (MI) regimes during a quantum quench for dimensions higher than one. In this talk, we focus on quenches within the MI regime and present our numerical results for the evolution of the two-point Green's function. We observed a light-cone-like spreading of single-particle correlations in both 1D and 2D and compare our estimated propagation velocities to existing experimental and theoretical work. We also discuss how our formalism can be easily extended to disordered systems, allowing for the study of Bose glass and possibly many-body-localized states. [Preview Abstract] |
Monday, March 13, 2017 3:30PM - 3:42PM |
C13.00004: Nonequilibrium Fractional Hall Response After a Topological Quench Nur Unal, Erich Mueller, M. O. Oktel When a system is suddenly driven between two topologically different phases, aspects of the original topology survive the quench, but most physical observables (edge currents, Hall conductivity) appear to be non-universal. I will present the non-equilibrium Hall response of a Chern insulator following a quench where the mass term of a single Dirac cone changes sign. In the limit where the physics is dominated by a single Dirac cone, we theoretically find that the Hall conductivity universally changes by two-thirds of the quantum of conductivity. I will analyze this universal behavior by considering the Haldane model, and discuss experimental aspects for its observation in cold atoms. [Preview Abstract] |
Monday, March 13, 2017 3:42PM - 3:54PM |
C13.00005: The inevitable power-law decay of quantum systems at long times: a dynamical criterion for predicting thermalization Marco Tavora, Jonathan Torres-Herrera, Lea Santos Any quantum system with a bounded spectrum shows a power-law decay of the survival probability at long times. Such time scales are accessible to experiments with cold atoms. We show that the value of the power-law exponent contains information about the spectrum, the initial state structure, and the number of particles that interact simultaneously. From this value, we infer the degree of delocalization of the initial state in the energy eigenbasis and therefore determine whether it can thermalize or not. Our analysis is developed for integrable and chaotic, interacting and non-interacting, clean and disordered isolated lattice many-body quantum systems. The initial states considered can be prepared in current experiments with cold atoms and ion traps. [Preview Abstract] |
Monday, March 13, 2017 3:54PM - 4:06PM |
C13.00006: Emergent quasi-integrals of motion in a non-integrable quantum spin chain Cheng-Ju Lin, Olexei Motrunich We study translationally-invariant operators which approximately commute with the Hamiltonian of a non-integrable quantum spin chain, using the technique of so-called "slow operators" developed in H. Kim et. al., Phys. Rev. E 92, 012128. In the strong coupling limit, the slow operator can be understood using the local Schrieffer-Wolff transformation and appears to be localized or at least quasi-localized. The existence of such an operator indicates possibility of a partial breakdown of the eigenstate thermalization hypothesis (ETH). [Preview Abstract] |
Monday, March 13, 2017 4:06PM - 4:18PM |
C13.00007: Emergent Hamiltonian description for dynamics of interacting integrable models Ryan Cadigan, Deepak Iyer Recent work has shown that in some cases the time evolution of a quantum state after a quench is equivalent to one of the eigenstates of an ``emergent'' Hamiltonian where the time enters as a coupling parameter. Here, we study the dynamical behavior of integrable models on a one-dimensional lattice starting from spatially localized initial states using such an effective description, as well as directly, and show the equivalence explicitly. We further study the development of correlations and entanglement in these time evolving states. [Preview Abstract] |
Monday, March 13, 2017 4:18PM - 4:30PM |
C13.00008: Exact Quench Dynamics of Open System Kondo Model Roshan Tourani, Natan Andrei Motivated by recent cold atom experiments, we consider the quench dynamics in the Kondo system consisting of a Fermi sea (the lead) coupled via spin exchange to spin-1/2 impurity. Starting from an initial state where the lead and the impurity are decoupled, we calculate the time evolution of the system after the coupling is turned on. As an observable we compute the expectation value of impurity spin as a function of time. Moreover, we will discuss the ongoing efforts on computing the Loschmidt echo. [Preview Abstract] |
Monday, March 13, 2017 4:30PM - 4:42PM |
C13.00009: Spatiotemporal correlation buildup after an interaction quench in the Luttinger model Nils O. Abeling, Stefan Kehrein We study the evolution of density-density correlations at different times and distances in the exactly solvable Luttinger model after a sudden quench from the ground state. We discuss the difference between correlations and susceptibilities, and how these results can be interpreted from the point of view of Lieb-Robinson bounds. For the correlation functions we specifically show that pre-quench entanglement in the ground state leads to algebraically decaying long distance tails outside the light cone. [Preview Abstract] |
Monday, March 13, 2017 4:42PM - 4:54PM |
C13.00010: Relaxation via phase-space mixing in integrable few-mode systems Ranchu Mathew, Eite Tiesinga Recently, quenches in isolated quantum systems have become a subject of intense study. We consider quantum few-mode systems that are integrable in their classical mean-field limit and become dynamically unstable after a quench of a system parameter. Specifically, we study a BEC in a double-well potential and a antiferromagnetic spinor BEC constrained to a single spatial mode. We study the time dynamics after the quench within the truncated Wigner approximation and find that due to phase-space mixing the system relaxes to a steady state. Using action-angle formalism, we obtain analytical expressions for the time evolution of expectation of observables and their long-time values. We find that the deviation of the long-time expectation value from its classical value scales as $(\ln N)^{-1}$, where $N$ is the number of atoms. Furthermore, the relaxation is Gaussian in time with a time constant which scales as $(\ln N)^2$. We confirm these results numerically. [Preview Abstract] |
Monday, March 13, 2017 4:54PM - 5:06PM |
C13.00011: Limit Cycles and Chaos via Quasi-periodicity in Two Coupled Ensembles of Ultra-cold Atoms. Aniket Patra, Emil Yuzbashyan, Boris Altshuler We study the dynamics of two mesoscopic ensembles of ultra-cold two level atoms, which are collectively coupled to an optical cavity and are being pumped incoherently to the excited state. Whereas the time independent steady states are well understood, little is known about the time dependent ones. We explore and categorize various time dependent steady states, e.g. limit cycles and chaotic behavior. We draw a non-equilibrium phase diagram indicating different steady-state behaviors in different parts of the parameter space. We discuss the synchronization of the two ensembles in the time dependent steady states. We also show the onset of chaos via quasi-periodicity. The rich time dependent steady-state behavior, especially the existence of chaos, opens up possibilities for several engineering applications. [Preview Abstract] |
Monday, March 13, 2017 5:06PM - 5:18PM |
C13.00012: Anomalous conduction property in an attractively-interacting Fermi gas Shun Uchino, Masahito Ueda A strongly-interacting Fermi gas realized with ultracold atoms has attracted attention due to similarities to neutron stars and high-temperature superconductors. A new aspect of studies in such a system is to understand its nonequilibrium property through the transport that has been examined with a two-terminal setup realized by the Tilman Esslinger's group at ETH. In this talk, I will discuss its transport property through a quantum point contact. In the absence of an interaction, it is known that the conductance is quantized, which is nothing but Landauer's formula. However, in the presence of an interaction, we show that near the superfluid transition temperature, the conductance can be enhanced by superfluid fluctuations. There, fluctuation-pair transport is essential, which has been overlooked in previous studies. Our results are consistent with the experimental observations. [Preview Abstract] |
Monday, March 13, 2017 5:18PM - 5:30PM |
C13.00013: Boundaries in a bosonized language Nayana Shah, Carlos Bolech We have been reexamining the Bosonization-Debosonization (BdB) procedure for systems including certain types of localized features, junctions and impurities being the two most conspicuous examples. We will present the latest developments in our attempts to assure BdB-based calculations are consistent. Our initial focus on the case of a tunneling junction out of equilibrium showed that the conventional approach to BdB gives results that are not consistent with the exact solution of the problem, even at the qualitative level, and highlighted inconsistencies that can adversely affect results in all types of calculations. We subsequently introduced a procedure that we developed to resolve these problems and argued that the framework should be widely applicable [1]. We substantiated the claim by applying the updated procedure to the two-lead Kondo problem [2], which besides being a key theoretical prototype of a strongly correlated system away from equilibrium, is also of immediate experimental relevance in many ways. Follow up calculations are helping to contextually demarcate the need for assuring consistency when doing calculations in bosonized problems. // [1] N. Shah and C. J. Bolech, Phys. Rev. B 93, 085440 (2016); [2] C. J. Bolech and N. Shah, Phys. Rev. B 93, 085440 (2016). [Preview Abstract] |
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