Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S25: BoseEinstein Condensates, Matter Optics, Atomic Interferometry, and Nonlinear WavesFocus

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Sponsoring Units: DAMOP Chair: Nathan Lundblad, Bates College Room: BCEC 160A 
Thursday, March 7, 2019 11:15AM  11:27AM 
S25.00001: Microgravity experiments with radiofrequencydressed BoseEinstein condensates aboard NASA's Cold Atom Laboratory Nathan Lundblad, Maxwell Gold, Xiaole Jiang, Ryan Carollo Microgravity conditions present opportunities for studying ultracold atomic systems free of gravitational perturbation. One such opportunity is the study of shell or bubblelike BoseEinstein condensates, which have not been observed terrestrially due to gravitational effects dominating condensate meanfield energy in typical experimental conditions. We present recent measurements using NASA's Cold Atom Laboratory facility aboard the International Space Station focusing on both preliminary characterization of the CAL atomchip magnetic trap and on the physics of radiofrequency (rf) dressed magnetic traps in a microgravity environment, and discuss model predictions of bubbleBEC properties in such an environment. 
Thursday, March 7, 2019 11:27AM  11:39AM 
S25.00002: Proposal for measuring Big G using the NASA Cold Atom Lab aboard the International Space Station Colson Sapp, Charles W Clark, Mark Edwards We propose an atom interferometry (AI) experiment to measure Big G constant in a microgravity environment. Our experiment is assumed to be conducted in NASA's Cold Atom Laboratory currently deployed to the International Space Station. The idea is to carry out an AI sequence many times, first with a source mass present and then with no source mass. The basic AI sequence is to split a BoseEinstein condensate (BEC) into two pieces using pulsed optical lattice potentials. These pieces fly apart in the presence of an harmonic potential and finally stop after one quarter trap period. The trap is then turned off for a wait time. The pieces acquire a relative velocity difference due to the differential gravitational pull of the source mass. The trap is turned back on and the pieces then recombine and are split again. The result is two clouds left nearly motionless near the trap center creating an interference pattern due to their relative velocity. We have simulated this sequence using the Lagrangian Variational Method (LVM) where the trial wave function is a sum of Gaussian clouds. We show how big G can be extracted from the interference pattern that results and present an approximate error budget for the measurement. 
Thursday, March 7, 2019 11:39AM  11:51AM 
S25.00003: Measurement induced dynamics and defect stabilization in spinor condensates Hilary Hurst, I. B. Spielman Weakly measuring manybody systems and allowing for feedback in real time can simultaneously create and measure new phenomena in quantum systems. We study weak measurement and classical feedback in spinor BoseEinstein condensates, focusing on the tradeoff between usable information obtained from measurement and quantum backaction. As a prototype example, we consider the dynamics of a domain wall in a twocomponent BEC and show that quantum backaction due to measurement causes two primary effects: domain wall diffusion and overall heating. The system dynamics and signaltonoise ratio depend on the choice of measurement observable. We describe a feedback protocol to create and stabilize a domain wall in the regime where domain walls are unstable, giving a prototype example of Hamiltonian engineering using measurement and feedback. Finally, we discuss extensions of this idea to higher spin systems. 
Thursday, March 7, 2019 11:51AM  12:03PM 
S25.00004: Nonthermal fixed points in a onedimensional antiferromagnetic spinor Bose gas Kazuya Fujimoto, Ryusuke Hamazaki, Masahito Ueda Recently, a nonthermal fixed point (NFTP) is proposed as a universal thermalization scenario [1], where a system evolving from a nonequilibrium initial state is attracted to the NTFP and shows a universal dynamical scaling law. We theoretically study quench dynamics in a onedimensional (1D) antiferromagnetic (AF) spinor Bose gas, finding universal thermalization dynamics characterized by a NTFP induced by two types of solitons. One soliton is a magnetic soliton having a locally magnetized part, and the other is an exotic bound state of magnetic solitons, which we refer to as a Flemish string because of the twisted magnetic structure. We numerically find that the stable magnetic solitons can disappear through formation of the Flemish strings, and that the cooperative soliton dynamics through the Flemish string promotes the relaxation. Then, we elucidate the dynamical scaling regarded as a signature of the NTFP in the quench dynamics. Furthermore, studying the experiment for a trapped 1D AF Bose gas [2], we find that the universal thermalization with the NTFP appear if the applied filed is quenched more strongly compared with the experiment. 
Thursday, March 7, 2019 12:03PM  12:15PM 
S25.00005: Universal relations and Tan contact matrix for 1D spinor quantum gases Shah Saad Alam, Han Pu The Tan contact and associated Tan relations, such as the tail of the momentum distribution, have been previously studied for a few kinds of spinor quantum gases, such as spinzero/half fermions, bosons, SU(N) symmetric cases or multicomponent gases. Inspired by our previous work on interacting spinor quantum gases with arbitrary spins, we present results of our investigation of the Tan contact matrix and its connection to the large momentum tail for arbitrary spin cases with spindependent interactions at arbitrary strengths. We further discuss the connection of the Tan contact matrix to two body density matrices, energetics and other universal relations. 
Thursday, March 7, 2019 12:15PM  12:27PM 
S25.00006: Supercurrent induced by multipoles in nonmagnetic spin2 BoseEinstein condensates Emi Yukawa, Masahito Ueda In spinor BoseEinstein condensates (BECs), a supercurrent is known to be induced by the magnetic degrees of freedom when the magnitude of the spin vector is finite. On the other hand, when a spinor BEC is nonmagnetic, the supercurrent originatingfrom the magnetic degrees of freedom is absentfor a spin1 BEC; however, it has remained to beclarified if it is essentially zero for any spin degrees of freedom. We show that a supercurrent can be induced by magnetic multipoles for a nonmagnetic spin2 BEC. We analytically derive asuperfluid in a nonmagnetic spin2 BEC that involves components originatingfrom the magnetic degrees of freedom. We also numerically demonstrate that these components can be induced by aspatially dependent magnetic field via the quadratic Zeeman effect. 
Thursday, March 7, 2019 12:27PM  12:39PM 
S25.00007: Internal oscillations of a darkbright soliton in a harmonic potential Majed Alotaibi, Lincoln Carr We investigate the dynamics of a darkbright soliton in a harmonic potential using a meanfield approach via coupled nonlinear Schrodinger equations appropriate to multicomponent BoseEinstein condensates. We use a modified perturbed dynamical variational Lagrangian approximation, where the perturbation is due to the trap, taken as a ThomasFermi profile. The wave function ansatz is taken as the correct hyperbolic tangent and secant solutions in the scalar case for the dark and bright components of the soliton, respectively. We also solve the problem numerically with pseudospectral Runge–Kutta methods. We find, analytically and numerically, for weak trapping the internal modes are nearly independent of center of mass motion of the darkbright soliton. In contrast, in tighter traps the internal modes couple strongly to the center of mass motion, showing that for darkbright solitons in a harmonic potential the center of mass and relative degrees of freedom are not independent. This result is robust against noise in the initial condition and should, therefore, be experimentally observable. 
Thursday, March 7, 2019 12:39PM  12:51PM 
S25.00008: Collision of BoseEinstein Condensates Fabio Lingua, Luca Lepori, Francesco Minardi, Vittorio Penna, Luca Salasnich We study the collision of two interacting BoseEinstein Condensates of ^{87}RB and ^{41}K in a weak harmonic confinement. The study is performed by means of numerical solution of two coupled Gross Pitaevskii equations. The process is investigated in presence of both attractive and repulsive interaction between the two atomic components, showing various complex phenomena such as the formation of dark and bright solitons, condensate trapping, and coupled oscillations of boson populations. 
Thursday, March 7, 2019 12:51PM  1:03PM 
S25.00009: Filamentary Dynamics of Dark Solitons, Vortex Rings and Knots Panayotis Kevrekidis In the present talk, we will revisit some principal excitations in selfrepulsive BoseEinstein condensates, namely dark solitons, vortex rings and knots. For dark solitons, upon introducing them and explaining their existence and stability properties in 1d, we will extend them both in the form of stripes and in that of rings in twodimensions, presenting an alternative (adiabaticinvariant based) formulation of their stability and excitations. We will explore their filamentary dynamics, as well as the states that emerge from their transverse (snaking) instability. Then, we will consider these structures even in three dimensions, in the form of planar, as well as spherical shell solitons and generalize our adiabatic invariant formulation there. We will show how the formalism can be extended to the case of vortex rings and their own filamentary dynamics. 
Thursday, March 7, 2019 1:03PM  1:15PM 
S25.00010: Lattice and continuum model for ultracold atoms in a crossedcavity system Poornima Shakya, Amulya Ratnakar, Sankalpa Ghosh Recent experiments by ETH and MIT groups have reported on the formation of a supersolid, respectively in scalar and spinorial ultracold atomic systems, an enigmatic phase of matter that shows superfluidity and solidlike density modulation, simultaneously. In this paper [1], we derive the extended BoseHubbard Hamiltonian for a BoseEinstein condensate loaded in a crossedcavity setup. Subsequently, in the continuum limit, we obtain the GrossPitaevskii energy functional and the GrossPitaevskii equations for the superfluid order parameters for such a supersolid phase and discuss its significance. 
Thursday, March 7, 2019 1:15PM  1:27PM 
S25.00011: Production of smooth flow in racetrack BECs at zero and nonzero temperatures Benjamin Eller, Daniel Fogarty, Charles W Clark, Mark Edwards We have studied the production of smooth, persistent currents in ultracold (bosonic) gas systems that consist of an atomic BEC and a noncondensate cloud. The BEC is assumed to be strongly confined in a horizontal plane by a vertical harmonic trap and, within this plane, subjected to an arbitrary twodimensional potential. The racetrack potential is made up of two straight parallel channels connected on both ends by semicircular channels of the same width and energy height as the straightaways. The zerotemperature behavior of the system is simulated using the GrossPitaevskii equation and at nonzero temperature by the ZarembaNikuniGriffin model. The flow is realized by stirring along the channel with a rectangular barrier. We conducted simulations of stirring racetrack BECs for a range of different racetrack geometries, barrier speeds and maximum energy heights both at zero and nonzero temperatures. We also investigated the mechanism for producing flow in order to be able to predict the amount of flow and its onset using a 1D model. We will present the results of the simulations and also discuss the effect of temperature on the amount of flow produced. 

S25.00012: ABSTRACT WITHDRAWN

Thursday, March 7, 2019 1:39PM  1:51PM 
S25.00013: Dimensional phase transitions from 1D quantum liquids to 3D condensates Sebastian Eggert, Imke Schneider, Axel Pelster, Polina Matveeva, Denis Morath, Dominik Strassel We consider weakly coupled strongly interacting quantum chains, such as quantum wires, anisotropic ultracold gases, or quasi1D spinchain compounds. It is known that a phase transition from the 1D Luttinger liquid behavior to a 3D ordered states can be qualitatively descibed by a chain mean field theory to determine the critical temperature, but the quantitative corrections and the range of validity is not well established. We therefore simulate the transition using a fully 3D microscopic model with very large scale quantum Monte Carlo calculations and compare with theoretical prediction including higher order terms in the chain mean field theory. We not only determine the very strong quantitative corrections, but also find a new regime of low density behavior where long range quantum correlations between the chains dominate the behavior, which leads qualitatively different powerlaws as a function of interchain couplings. 
Thursday, March 7, 2019 1:51PM  2:03PM 
S25.00014: Robust cat state from kinetic driving of a boson gas Fernando Sols, Gregor Pieplow, Charles E. Creffield We investigate the behavior of a onedimensional BoseHubbard gas whose kinetic energy is made to oscillate with zero timeaverage. The effective dynamics is governed by an atypical manybody Hamiltonian where only evenorder hopping processes are allowed. In some parameter range the system has similarities to the Richardson model, which permits a detailed understanding of its key features. The ground state is a catlike superposition of two macroscopically occupied oneatom states of opposite momentum. Interactions give rise to a reduction (or modified depletion) cloud that is common to both macroscopic options. Symmetry arguments permit a precise identification of the two orthonormal, macroscopically distinguishable manybody states yielding the cat state, each involving a large number of momentum configurations. For a gas between hard walls, the cat correlations are fundamentally robust because the system cannot collapse into a nonzero current state. 
Thursday, March 7, 2019 2:03PM  2:15PM 
S25.00015: Emergence of correlations in the process of thermalization of interacting bosons Fausto Borgonovi, Felix Izrailev The relevance of thermalization to the increase of correlations in the quench dynamics of an isolated system with a finite number of interacting bosons has been studied. Specifically, we analyze how correlations between occupation numbers increase in time resulting in the emergence of the BoseEinstein distribution. Before saturation, the twopoint correlation function increases quadratically in time (as predicted by perturbation theory), while the outoftimeorder correlator (OTOC) increases algebraically with an exponent 2.5 beyond the perturbative region. Our results, that can be confirmed experimentally in traps with interacting bosons, may be also relevant to the problem of black hole scrambling. 
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