Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E19: Precision Many Body Physics IVFocus

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Sponsoring Units: DAMOP Chair: Tigran Sedrakyan, University of Massachusetts Amherst Room: BCEC 156C 
Tuesday, March 5, 2019 8:00AM  8:36AM 
E19.00001: Quantum Transport in Strongly Interacting Fermi Gases Invited Speaker: Martin Zwierlein Transport is the defining property of states of matter, but often the most difficult to understand. Strongly interacting Fermi gases are especially challenging, despite their ubiquitous presence across many fields of physics. Experiments on ultracold fermionic atoms allow the direct measurement of transport properties in ideal model systems where the hamiltonian is precisely known while transport properties are difficult to calculate theoretically. 
Tuesday, March 5, 2019 8:36AM  8:48AM 
E19.00002: Spectra of heavy polarons and molecules coupled to a Fermi sea Dimitri Pimenov, Moshe Goldstein We study the spectrum of an impurity coupled to a Fermi sea (e.g., minority atom in an ultracold gas, exciton in a solid) by attraction strong enough to form a molecule/trion. We introduce a diagrammatic scheme which allows treating a finite mass impurity while reproducing the Fermi edge singularity in the immobile limit. For large binding energies the spectrum is characterized by a semicoherent repulsive polaron and an incoherent molecule, which is the lowestenergy feature in the singleparticle spectrum. The previously predicted attractive polaron seems not to exist for strong binding. 
Tuesday, March 5, 2019 8:48AM  9:00AM 
E19.00003: Energy and shortrange correlations of Bose Polarons in the strong coupling regime Carsten Robens, Zoe Yan, Yiqi Ni, Alexander Yu Chuang, Martin Zwierlein The concept of the Bose polaron quasiparticle originates in Landau’s description of a crystal’s conduction electron which deforms the surrounding ionic lattice. Despite the conceptual simplicity of the Bose polaron – i.e. an impurity dressed by a surrounding bosonic bath – this quasiparticle poses remarkable challenges for both theoretical and experimental physicists. These challenges arise at strong interaction strengths where a multitude of bosons can simultaneously interact with the impurity thereby forming a complicated manybody state. We here report on the first creation of an ensemble of Bose polarons – comprised of fermionic ^{40}K impurities immersed in a ^{23}Na Bose Einstein condensate – in local equilibrium and in the strongly interacting regime. Using radio frequency ejection spectroscopy, we measure the Bose polaron groundstate energy and shortrange correlations as a function of temperature across a variety of interaction strengths by tuning an interspecies magnetic Feshbach resonance. We further study collective oscillations between the BEC and the impurities, demonstrating strong dissipation of the impurities’ momentum at the transition from collisionless to hydrodynamic regime. 
Tuesday, March 5, 2019 9:00AM  9:12AM 
E19.00004: Polaron mobility in the ``beyond quasiparticles" regime Andrey Mishchenko In a number of physical situations, from polarons, to nonFermi liquids, to Dirac liquids, 
Tuesday, March 5, 2019 9:12AM  9:24AM 
E19.00005: The contact of the Fermi gas at unitarity Scott Jensen, Christopher Gilbreth, Yoram Alhassid The unitary Fermi gas is a strongly correlated system with a shortrange interaction that saturates the upper bound on the modulus of the twoparticle swave scattering amplitude. It is characterized by an infinite scattering length and sits in the middle of the BCSBEC crossover. The contact of this system is a quantity that describes shortrange pairing correlations and appears in the high momentum tail of the momentum distribution and the static structure factor, as well as in the highfrequency tail of the shear viscosity spectral function. There have been a number of recent calculations and important experimental advances towards determining the contact for the unitary Fermi gas. We present results for the temperature dependence of the contact at unitarity using finitetemperature auxiliaryfield quantum Monte Carlo (AFMC) methods on the lattice. Our calculations are carried out within the canonical ensemble with multiple filling factors and extrapolated to the continuum limit. We compare our results with other theoretical calculations and with experiment. 
Tuesday, March 5, 2019 9:24AM  9:36AM 
E19.00006: WITHDRAWN ABSTRACT

Tuesday, March 5, 2019 9:36AM  9:48AM 
E19.00007: Spin Transport in a Mott Insulator of Ultracold Fermions Matthew A Nichols, Lawrence Cheuk, Melih Okan, Thomas Hartke, Enrique Mendez, Hao Zhang, Ehsan Khatami, Martin Zwierlein Understanding transport in strongly interacting Fermi systems is among the most pressing but difficult tasks of manybody physics. The FermiHubbard model serves as a prototypical example of a strongly correlated fermionic quantum system, and is believed to hold the key to hightemperature superconductivity. However, the transport properties in the various regions of its phase diagram are far from understood. We realize the FermiHubbard model using a gas of fermionic atoms in an optical lattice, confined in a homogeneous box trap. In this setting, we study spin and charge transport using a quantum gas microscope, able to resolve individual atoms. In particular, at half filling, the charge degree of freedom is frozen, while spins are still able to move. Spin transport is induced by applying a spindependent magnetic field gradient. We observe spin dynamics which are diffusive in nature, and obtain the spin conductivity and spin diffusivity. These findings can be compared to existing theoretical approaches, such as the numericallinkedcluster expansion (NLCE). 
Tuesday, March 5, 2019 9:48AM  10:00AM 
E19.00008: Excitation spectrum of dipolar Bose gases Youssef Kora, Massimo Boninsegni We investigate the excitation spectrum of a dipolar Bose gas in the low temperature limit across the superfluidsupersolidcrystal transition. At sufficiently low temperatures, a system of aligned dipolar bosons will undergo a quantum phase transition by tuning the range of the repulsive twobody potential. In one limit, the phase of the system is that of a classical crystal of filaments. At the other limit, the system experiences quantum melting into a superfluid phase. In the intermediate regime, the system exists in a supersolid state. We use Quantum Monte Carlo techniques to compute imaginary time correlation functions at the different regions of the phase diagram, and we use the method of Maximum Entropy to extract the dynamical structure factor, which is then used to obtain the excitation spectrum and its evolution throughout the phase diagram. 
Tuesday, March 5, 2019 10:00AM  10:12AM 
E19.00009: Bose liquid in checkerboard antiferromagnet Haiyuan Zou, Fan Yang, Wei Ku The frustrated J_{1}J_{2} antiferromagnet model on the checkerboard lattice, known as the twodimensional analog of the pyrochlore lattice, provides a perfect platform for dimensional crossover effect due to competition between the two exchange constants J_{1} and J_{2}. Using recently developed tensor network algorithm based on Projected Entangled Simplex States (PESS), we obtain a line degenerate bose liquid state without magnetic order on the whole range of J_{2} > J_{1} for both XY and Heisenberg antiferromagnetic limit. The degenerate liquid state is stable even when small anisotropy on J_{1} bond is introduced and the interaction enhance the robustness of the bose liquid behavior. 
Tuesday, March 5, 2019 10:12AM  10:24AM 
E19.00010: Impenetrable SU(N) fermions in onedimensional lattices Yicheng Zhang, Lev Vidmar, Marcos Rigol We study SU(N) fermions in the limit of infinite onsite repulsion between all species. We focus on states in which every pair of consecutive fermions carries a different spin flavor. Since the particle order cannot be changed (because of the infinite onsite repulsion) and contiguous fermions have a different spin flavor, we refer to the corresponding constrained model as the model of distinguishable quantum particles. We introduce an exact numerical method to calculate equilibrium onebody correlations of distinguishable quantum particles based on a mapping onto noninteracting spinless fermions. In contrast to most manybody systems in one dimension, which usually exhibit either powerlaw or exponential decay of offdiagonal onebody correlations with distance, distinguishable quantum particles exhibit a Gaussian decay of onebody correlations in the ground state, while finitetemperature correlations are well described by stretched exponential decay. We also study the dynamics of distinguishable quantum particles after geometric quantum quenches. 
Tuesday, March 5, 2019 10:24AM  10:36AM 
E19.00011: Efficient exact diagonalization of the nbody reduced density matrix Hatem Barghathi, Adrian Del Maestro The nbody reduced density matrix provides an alternate description of a quantummany body system that can offer considerable compression over the wavefunction while providing access to observables and correlation functions. In this talk, we present an efficient algorithm for its construction and exact diagonalization in a system of N interacting particles. In one spatial dimension, we simplify computations by exploiting translational, reflection and particlehole symmetries. We illustrate the method by calculating the maximal particle entanglement entropy constructed from the N/2particle reduced density matrix in the ground state of up to 13 interacting fermions on 26 sites. 
Tuesday, March 5, 2019 10:36AM  10:48AM 
E19.00012: Prethermalization and Thermalization in Generic Isolated Quantum Systems Krishnanand Mallayya, Marcos Rigol, Wojciech De Roeck Prethermalization has been extensively studied in systems close to integrability. We propose a more general, yet simpler, setup for this phenomenon. We consider a possibly nonintegrable reference dynamics, weakly perturbed so that the perturbation violates at least one conservation law of the reference dynamics. We argue then that the evolution of the system proceeds via intermediate (generalized) equilibrium states of the reference dynamics. The motion on the manifold of equilibrium states is governed by an autonomous equation, flowing towards global equilibrium in a time of order g^{2}, with g the perturbation strength. We also describe the leading corrections to the timedependent reference equilibrium state, in general of order g. The theory is wellconfirmed by numerical calculations relying on the numerical linked cluster expansion. 
Tuesday, March 5, 2019 10:48AM  11:00AM 
E19.00013: Evolution of twotime correlations in strongly correlated dissipative systems: aging and hierarchical dynamics Stefan Wolff, JeanSebastien Bernier, Dario Poletti, Ameneh Sheikhan, Corinna Kollath In recent years, considerable experimental efforts have been devoted 
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