Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A24: Strongly Interacting Quantum Fermi and Bose Gases |
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Sponsoring Units: DAMOP Chair: Bo Zhen, University of Pennsylvania Room: BCEC 159 |
Monday, March 4, 2019 8:00AM - 8:12AM |
A24.00001: Probing the many-body physics via measurement of the closed-channel fraction in a ^{6}Li superfluid Qijin Chen, Xing-Can Yao, Xiang-Pei Liu, Hao-Ze Chen, Xiao-Qiong Wang, Yu-Xuan Wang, Yu-Ao Chen, Kathryn Levin, Jian-Wei Pan Atomic Fermi gases provide an ideal platform for studying the pairing and superfluid physics, utilizing a Feshbach resonance between closed channel molecular states and open channel scattering states. The closed-channel fraction Z contains important many-body interacting effects. Here we probe the many-body physics of interacting Fermi gases of ^{6}Li by measuring Z in the entire system. We have observed a significant departure from two-body physics. Away from |
Monday, March 4, 2019 8:12AM - 8:24AM |
A24.00002: Comparative Study of One-Dimensional Bose and Fermi Gases with Contact Interactions Yuta Sekino, Shina Tan, Yusuke Nishida One-dimensional spinless Bose and Fermi gases with contact interactions have the close relationship via Girardeau’s Bose-Fermi mapping, leading to the correspondences in their energy spectra and thermodynamics. However, correlation functions are in general not identical between these systems. We derive in both systems the universal relations for correlation functions, which hold for any energy eigenstate and any statistical ensemble of the eigenstates[1]. These relations include the large-momentum tails of static structure factors and of momentum distributions as well as energy relations, which connect the sums of kinetic and interaction energies to the momentum distributions. The relations involve two- and three-body contacts, which measure local two- and three-body correlations, respectively. We clarify how the relations for bosons and fermions differ and are connected with each other. In particular, we find that the three-body contact makes no contribution to the bosonic energy relation, but it plays a crucial role in fermionic one. |
Monday, March 4, 2019 8:24AM - 8:36AM |
A24.00003: Ultracold Gas of NaLi Molecules in the Triplet Ground State Juliana Park Ultracold gases of molecules allow us to study short-range chemical reactions, novel quantum phases, and quantum information processing. The NaLi molecule, the lightest bi-alkali molecule, in the triplet ground state has permanent electric and magnetic dipole moments and is predicted to have a small universal loss rate leading to long collisional lifetime. This enables us to investigate the complexity of chemical reactions by finding links to scattering theory. Also, with the aid of tunable long-range interactions between the molecules, we can explore the possibility of quantum simulation of many-body physics. We have previously achieved the long-lived triplet ground state molecules in an optical dipole trap through a two-step process: formation of Feshbach molecules and stimulated rapid adiabatic passage. We report results of recent studies with our triplet state molecules including the observation of long lifetime of the molecules in a longer wavelength optical dipole trap. |
Monday, March 4, 2019 8:36AM - 8:48AM |
A24.00004: An improved Lieb-Robinson bound for many-body Hamiltonians with power-law interactions Francisco Machado, Dominic Else, Chetan Nayak, Norman Yao The Lieb-Robinson bound limits the velocity of the spread of information in non-relativistic short-range interacting quantum systems, inducing a notion of speed of light. More specifically, it proves that, under time evolution, any local operator remains confined (up to exponentially decaying tails) to a region whose radius grows linearly with time. Motivated by experimental platforms such as ion traps, Rydberg atoms and spin defects in solids, recent work has investigated such bounds in long-range interacting systems, where the interaction strength decays as a power-law of the distance. In these results, the extent of the time evolved local operator is characterized by power-law tails and one obtains a power-law light-cone. In this talk, we introduce a new notion of light-cone for power-law interacting systems that induces a more stringent definition of locality. We prove new Lieb-Robinson bounds for multi-body interacting systems which improve the spatial decay profile of the time evolved local operator and thus lead to a better light-cone. These improvements enable the proof of the existence of a long-lived prethermal regime in long-range interacting systems. |
Monday, March 4, 2019 8:48AM - 9:00AM |
A24.00005: Quantum phases of many-body dipolar system in one dimension Niraj Ghimire, Susanne F Yelin We study the zero temperature quantum phases of dipoles in a quasi-one-dimensional zigzag chain. Since the dipole-dipole interaction is long-range, a dipolar many-body system is predicted to feature intriguing phases. We investigate the many-body effects in this model using the Density Matrix Renormalization Group (DMRG) method. |
Monday, March 4, 2019 9:00AM - 9:12AM |
A24.00006: Efimov Enhanced Kondo Effect in Alkaline and Alkaline-Earth Atomic Gas Mixture Juan Yao, Hui Zhai, Ren Zhang Recent experiment has observed Feshbach resonances between alkaline and alkaline-earth atoms. These Feshbach resonances are insensitive to the nuclear spin of alkaline-earth atoms. Utilizing this feature, we propose to take this system as a candidate to perform quantum simulation of the Kondo effect. An alkaline atom can form a molecule with an alkaline-earth atom with different nuclear spins, which plays the role of spin-exchange scattering responsible for the Kondo effect. Furthermore, we point out that the existence of three-body bound state and atom-molecule resonance due to the Efimov effect can enhance this spin-exchange scattering, and therefore enhance the Kondo effect. We discuss this mechanism first with a three-body problem in free space, and then demonstrate that the same mechanism still holds when the alkaline atom is localized by an external trap and becomes an impurity embedded in the alkaline-earth atomic gases. |
Monday, March 4, 2019 9:12AM - 9:24AM |
A24.00007: Asymmetric Conductivity as a Manifestation of Kondo Effect in Cold Atom Yanting Cheng, Xin Chen, Zhigang Wu, Ren Zhang Motivated by recent theoretical and experimental advances in the quantum simulation of alkaline |
Monday, March 4, 2019 9:24AM - 9:36AM |
A24.00008: Low Energy Excitation Spectra from Tangent Plane Methods, Part I Tommaso Guaita Variational methods are extensively used in quantum many body problems to overcome the exponential growth of the Hilbert space with the system size. By focusing on a suitable sub-manifold of states, we can study properties of ground states and low excited states. Here, we will introduce a novel framework to approximate the low lying energy spectrum by studying the linearized Hamiltonian flow on the tangent plane to this manifold at the ground state. |
Monday, March 4, 2019 9:36AM - 9:48AM |
A24.00009: Low Energy Excitation Spectra from Tangent Plane Methods, Part II Lucas Hackl Variational methods are extensively used in quantum many body problems to overcome the exponential growth of the Hilbert space with the system size. By focusing on a suitable sub-manifold of states, we can study properties of ground states and low excited states. Here, we will introduce a novel framework to approximate the low lying energy spectrum by studying the linearized Hamiltonian flow on the tangent plane to this manifold at the ground state. |
Monday, March 4, 2019 9:48AM - 10:00AM |
A24.00010: Generalized HydroDynamics on an Atom Chip Maximilian Schemmer, Isabelle Bouchoule, Benjamin Doyon, Jérôme Dubail I will present an experimental test of the new theory of Generalized HydroDynamics (GHD), introduced in 2016 to describe long wave-length dynamics of one-dimensional (1d) quantum integrable systems [1]. Integrable systems posses an infinite number of conserved quantities and GHD takes into account the conservation of all of them. We monitor the time evolution of the in situ density profiles of a single 1d cloud of bosonic atoms trapped on an atom chip after a quench of the longitudinal trapping potential. The weakly interacting atomic clouds lie at the crossover between the quasicondensate and the ideal Bose gas regimes. Predictions of GHD are in very good agreement with the experiment. Previously existing theories such as the “conventional” hydrodynamic approach, which relies on the assumption of local thermal equilibrium, described by a Gibbs ensemble, are unable to reproduce the experimental data. These results can be found in [3]. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A24.00011: Emergence of hydrodynamics in large driven quantum systems Bingtian Ye, Francisco Machado, Christopher White, Roger Mong, Norman Yao Many non-equilibrium dynamical properties of Floquet (driven) systems remain unclear. In particular, understanding the microscopic details of short-time thermalization as well as the cross-over to hydrodynamics and late-time Floquet heating remains an open challenge. We investigate the dynamics of Floquet systems using a novel numerical method termed 'density matrix truncation' (DMT). At small system sizes, we gauge the applicability and limitations of DMT via comparison with Krylov subspace methods; we demonstrate that DMT can capture both the prethermal state and the late-time thermalization to infinite temperature. Pushing DMT to larger system sizes (up to L = 100) enables us to confirm the exponential scaling of the Floquet heating time with driving frequency. Access to large systems allows us to directly study the emergence of late-time hydrodynamics. In particular, we implement a spatially inhomogeneous drive to probe the interplay between Floquet heating and the diffusion of local energy density. Despite the heating being a coherent quantum process, the emergent hydrodynamical behavior is captured by a simple classical diffusion equation. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A24.00012: Hydrodynamics of operator spreading and quasiparticle diffusion in interacting integrable systems (part I) Sarang Gopalakrishnan, David Huse, Vedika Khemani, Romain Vasseur We address the hydrodynamics of operator spreading in interacting integrable lattice models. In these models, operators spread through the ballistic propagation of quasiparticles, with an operator front whose velocity is locally set by the fastest quasiparticle velocity. In interacting integrable systems, this velocity depends on the density of the other quasiparticles, so equilibrium density fluctuations cause the front to follow a biased random walk, and therefore to broaden diffusively. Ballistic front propagation and diffusive front broadening are also generically present in non-integrable systems in one dimension; thus, although the mechanisms for operator spreading are distinct in the two cases, these coarse grained measures of the operator front do not distinguish between the two cases. Our results elucidate the microscopic mechanism for diffusive corrections to ballistic transport in interacting integrable models. |
Monday, March 4, 2019 10:24AM - 10:36AM |
A24.00013: Hydrodynamics of operator spreading and quasiparticle diffusion in interacting integrable systems (Part II) Vedika Khemani, Sarang Gopalakrishnan, David Huse, Romain Vasseur We address the hydrodynamics of operator spreading in interacting integrable lattice models. In these models, operators spread through the ballistic propagation of quasiparticles, with an operator front whose velocity is locally set by the fastest quasiparticle velocity. In interacting integrable systems, this velocity depends on the density of the other quasiparticles, so equilibrium density fluctuations cause the front to follow a biased random walk, and therefore to broaden diffusively. Ballistic front propagation and diffusive front broadening are also generically present in non-integrable systems in one dimension; thus, although the mechanisms for operator spreading are distinct in the two cases, these coarse grained measures of the operator front do not distinguish between the two cases. Our results elucidate the microscopic mechanism for diffusive corrections to ballistic transport in interacting integrable models. |
Monday, March 4, 2019 10:36AM - 10:48AM |
A24.00014: Hydrodynamics with Spacetime-dependent Scattering Length Keisuke Fujii, Yusuke Nishida Hydrodynamics provides concise but powerful description of long-time and long-distance physics of correlated systems out of thermodynamic equilibrium. Here we construct hydrodynamic equations for nonrelativistic particles with the spacetime-dependent scattering length and show that it enters constitutive relations uniquely so as to represent the fluid expansion and contraction in both normal and superfluid phases. As a consequence, we find that a leading dissipative correction to the contact density due to the spacetime-dependent scattering length is proportional to the bulk viscosity. Also, when the scattering length is slowly varied over time in a uniform system, the entropy density is found to be produced even without fluid flows in proportion to the bulk viscosity, which may be useful as a novel probe to measure the bulk viscosity in ultracold atom experiments. |
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