Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F02: Artificial Gauge Fields, SpinOrbit Coupling, and Optical Lattices 
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Sponsoring Units: DAMOP Chair: Marcos Rigol, Pennsylvania State University Room: 105 
Tuesday, March 3, 2020 8:00AM  8:12AM 
F02.00001: Vortices in Rotating BoseEinstein Condensate Shells Karmela Padavic, Kuei Sun, Courtney Lannert, Smitha Vishveshwara We present a study of superfluid vortices in rotating shellshaped BoseEinstein condensates (BECs). Hollow spherical BECs are of interest in connection to ongoing experimental efforts on the International Space Station and they naturally occur in optical lattice systems of ultracold bosons and interiors of neutron stars. Fundamentally, they have interesting geometry (nonzero curvature) and topology (hollow center). When BECs are rotated, discrete vortices are generated in pairs, as a consequence of the quantum coherence and the closed shape of the system. Using a meanfield approach, numerical solutions of the GrossPitaevskii equation and insights from classical fluid dynamics, we find that hollow condensates have a lower energy barrier to emergence of vortices than fully filled BECs. Further, we show that the rotation frequency at which nucleation of vortex lines is energetically favorable increases with BEC shell thickness. At this frequency the first vortex line is generated as straight and extends along the rotation axis. We consider the possibility of bent vortex lines (offaxis vortex pairs of opposite circulations in the twodimensional shell limit) and determine that they are unstable except at fast rotation. 
Tuesday, March 3, 2020 8:12AM  8:24AM 
F02.00002: Dynamics of Quantum Gas in NonAbelian Gauge Field Mehedi Hasan, Chetan Madasu, Chang Chi Kwong, Frédéric Chevy, David Wilkowski We experimentally realize SU(2)symmetric artificial gauge field with the tripod laser scheme. First, the nonAbelian nature of the artificial gauge field is revealed by performing loop operations, at different orders, in the parameter space [1]. It was found that the dynamics of internal states leads to a new thermometric scheme that exploits the interferometricdisplacement of atoms [1]. Afterwards, the coupling dynamics of internal( i.e., spin) and external(i.e., momentum)degrees of freedoms, in a twodimensional nonAbelian gauge field, is shown to exhibit an asymmetric expansion of the atomic cloud [2]. This spinorbitcoupled gas breaks the Galilean invariance and modifies the usual reflectionlaws, owing to its inherent peculiar dispersion relation. The density distribution of external dynamics markedly carries the signature of the nonAbelian nature of the underlying gauge field. 
Tuesday, March 3, 2020 8:24AM  8:36AM 
F02.00003: Quantum simulation of Dynamical gauge field for ultracold atoms in a cavity Sankalpa Ghosh, Poornima Shakya Quantum simulation of synthetic gauge field in ultracold atoms provides opportunity to realize the analogues of Landau levels of electrons and Quantum Hall Physics, HofstadterHarper Hamiltonian, and topological phases in a much more controlled environment. Where the initial studies were mostly on synthetic gauge fields that do not have dynamics of their own, a number of current studies aimed to create dynamical gauge field for neutral ultra cold atoms to extend the scope of such analogue quantum simulations for condensed matter and highenergy physics related phenomena. 
Tuesday, March 3, 2020 8:36AM  8:48AM 
F02.00004: Superfluidity and Bogoliubov excitations of a striped spinorbit coupled BEC induced by a weak optical lattice Guanqiang Li, Xiwang Luo, Junpeng Hou, Chuanwei Zhang We investigate the groundstate superfluidity and Bogoliubov excitations of a striped spinorbit coupled BoseEinstein condensate (BEC) with the momentumspace hopping induced by a weak optical lattice. The groundstate phase diagram and corresponding superfluid fraction are calculated for different system parameters. The Bogoliubov spectrum is studied and an exotic avoided band crossing between roton and Goldstone modes is revealed, which is very different from traditional spinorbit coupled BoseEinstein condensate with doublegapless Goldstone modes. We study the quantum depletion, which can be used to characterize the phase transitions. 
Tuesday, March 3, 2020 8:48AM  9:00AM 
F02.00005: Optical Vortex Braiding in Composite Bessels Andrew Voitiv, Jasmine Andersen, Mark Siemens, Mark T. Lusk We theoretically propose and experimentally demonstrate the braiding of optical vortices in a laser beam with more than 2π rotation by superposing Bessel modes with a plane wave. Laser beams containing a single, centered vortex with integervalued orbital angular momentum (OAM) have been extensively studied and engineered, but beams with two or more optical vortices have received less attention. Optical vortex braiding refers to the periodic rotation of two or more vortices around the central axis of propagation in a laser beam. Braiding is a topological feature in knot theory, but no physicallyrealizable scheme for optical vortex braiding beyond a ¼  rotation has been identified, much less experimentally demonstrated. In this work, we present a theoretical proposition for braiding optical vortices in Bessel beams, along with analytical expressions for the braiding trajectories and braiding period. We accompany this work with the experimental realization of vortex braiding in physical laser beams, using BesselGaussian beams. We show two vortices braiding completely three times, the most observed to our knowledge. 
Tuesday, March 3, 2020 9:00AM  9:12AM 
F02.00006: Spin Angular Momentum in Acoustic Field Theory Lucas Burns, Konstantin Y Bliokh, Justin Dressel We construct a Lagrangian representation of acoustic field theory that accounts for the local radiation forces and torques experienced by subwavelength probe particles, analogous to those experienced by Rayleigh particles in optical fields. The traditional acoustic Lagrangian representation with a scalar potential is unable to reproduce these measured effects. By introducing a displacement vector potential, analogous to the electromagnetic vector potential, we derive the appropriate local momentum and spin densities directly as conserved Noether currents. The results agree with those proposed in recent analyses of intrinsic acoustic spin and are consistent with recent experiments. 
Tuesday, March 3, 2020 9:12AM  9:24AM 
F02.00007: BoseEinstein condensation in effective HarperHofstadter bands: simulations of synthetic magnetic fields by optical lattice shaking Han Fu, Fnu Setiawan, Logan W Clark, Andreas Glatz, Kathryn Levin The cold atom field has been focused on generating topological and other exotic phases of quantum matter by, for example, creating strong 
Tuesday, March 3, 2020 9:24AM  9:36AM 
F02.00008: Inhomogeneous meanfield approach for collective modes at the superfluidMott glass transition Martin Puschmann, Jose A Hoyos, Thomas Vojta We employ an inhomogeneous meanfield approach plus Gaussian fluctuations to investigate disordered BoseHubbard models with particlehole symmetry in two and three dimensions. Within this framework, the collective excitations, i.e., Goldstone mode and the Higgs (amplitude) mode, are described by two effective, decoupled, disordered singleparticle Hamiltonians whose properties are determined by the underlying meanfield solution. Based on multifractal analysis, we investigate the localization properties of each mode separately as a function of energy and the distance from the superfluidMott glass transition. Furthermore, we calculate susceptibility functions and compare the results with Monte Carlo simulations and experiments. 
Tuesday, March 3, 2020 9:36AM  9:48AM 
F02.00009: Realizing Z_{2} phases and Majorana Spectroscopy in extended BoseHubbard systems Smitha Vishveshwara, David Minot Weld The connection between transverse XY spin chains and the fermionic Kitaev chain with nearestneighbor hopping and pairing has been well known for decades, and has lately drawn attention for its rich phase diagram and relevance to realizations of Majorana fermions. Here, we study the novel system comprised of a BoseHubbard chain connected to a reservoir that can generate analogous pairing terms for bosons. We describe a coldatom realization of such a system in a biased zigzag optical lattice. We show that in certain limits, the Bosonic Kitaev chain maps on to the XY spin chain, resulting in an unsual Z_{2} phase that has number fluctuation but no offdiagonal long range order associated with boson condensation. Noteworthy features include the possibility of a strongly correlated manybody qubit ground state and the potential for coldatom measurements of the Kitaev chain energy spectrum, including zeroenergy Majorana bound states. 
Tuesday, March 3, 2020 9:48AM  10:00AM 
F02.00010: Dark states of multilevel fermionic atoms in doublyfilled optical lattices Asier Pineiro Orioli, Ana Maria Rey We propose to use fermionic atoms with degenerate ground and excited internal levels (F_{g}→F_{e}), loaded into the motional ground state of an optical lattice with two atoms per lattice site, to realize dark states with no radiative decay. The physical mechanism behind the dark states is an interplay of Pauli blocking and multilevel dipolar interactions. The dark states are independent of lattice geometry, can support an extensive number of excitations and can be coherently prepared using a Raman scheme taking advantage of the quantum Zeno effect. These attributes make them appealing for atomic clocks, quantum memories, and quantum information on decoherence free subspaces. 
Tuesday, March 3, 2020 10:00AM  10:12AM 
F02.00011: Numerical study of antiferromagnetic nearestneighbor spin correlations of an SU(6) Fermi gas in an optical lattice Eduardo Ibarra Garcia Padilla, Kaden Hazzard, Richard Theodore Scalettar, HaoTian Wei, Shintaro Taie, Naoki Nishizawa, Yosuke Takasu, Yoshihito Kuno, Yoshiro Takahashi Experimental progress with ultracold alkalineearthlike atoms allows quantum simulation of novel phenomena and phases of matter. Many interesting SU($N$) phases are characterized by their magnetic correlations. Recently, the experiment at Kyoto has detected nearestneighbor antiferromagnetic (AFM) spincorrelations in an SU(6) $^{173}$Yb Fermi gas loaded in 1D, 2D and 3D optical lattices. Such systems are effectively described by the SU($N$) Fermi Hubbard Model. We have developed and applied the Exact Diagonalization and Determinant Quantum Monte Carlo methods to solve such model in all of the relevant geometries. With these tools we calculate the density, double occupancy, entropy and magnetic correlations in a trapped gas under the local density approximation. We compare the calculated and measured nearestneighbor AFM correlations, and we find they agree quantitatively. In 2D and 3D the experiments reach lower temperatures than is possible to accurately compute with theory, but in 1D, the temperature estimated from theory comparison is $k_BT/t = 0.08(2)$, being the lowest temperature ever reported for a Fermi gas in an optical lattice. 
Tuesday, March 3, 2020 10:12AM  10:24AM 
F02.00012: Dynamics of an almost lattice gauge theory realized by an ultracold atom system Daniel Gonzalez Cuadra, Valentin Kasper, Alexandre Dauphin, Philipp Hauke, Fred Jendrzejewski, Maciej Lewenstein Recently carried out experiments with ultracold atoms have realized the first building blocks to simulate lattice gauge theories quantum. Despite the great progress, the influence of experimental imperfections on the phase structure or the nonequilibrium dynamics is unclear. In this thesis we study the effect of terms violating the local gauge invariance as they occur in a typical experimental setup. In particular, we focus on ultracold atom setups which exploit angular momentum conservation in order to realize local gauge invariance. We also study the influence of dissipation in these systems and compare the dynamics of a theory with exact and almost lattice gauge theory. Especially we determine the time scales and observables when the difference between the two theories becomes significant. 
Tuesday, March 3, 2020 10:24AM  10:36AM 
F02.00013: Z_{2 }Lattice Gauge System and Dynamical Localization Zhiyuan Yao, Chang Liu, Pengfei Zhang, Hui Zhai Gauge theory has been playing a fundamental role in our understanding of the deepest mysteries of physics. And recent advances in cold atom physics have also made the study of dynamical gauge systems a new frontier. Using Floquet approach, we propose to realize a onedimensional Z_{2} lattice gauge model, featuring extensive local constants of motions, using two specifies of Rb atoms. The resulting Floquet Hamiltonian turns out to be quite simple. Within a given symmetry sector of good quantum numbers, the system can be viewed as a 1D transverse quantum Ising model with a binary random longitudinal field. Therefore, the dynamics of the system is essentially controlled by disordered Hamiltonians, implying that the system can feature many body localization (MBL) as a result of dynamical localization. Numerical studies of energy level statistics and quench dynamics clearly demonstrate the existence of MBL phase in this system. 

F02.00014: Unusual superfluid behavior of population imbalanced atomic Fermi gases in a twodimensional optical lattice Lin Sun, Qijin Chen We study the superfluid behavior of population imbalanced ultracold atomic Fermi gases with a short range attractive interaction in a twodimensional optical lattice (2DOL), using a pairing fluctuation theory, within the context of BCSBEC crossover. We find that population imbalance now has highly unusual effects on the behavior of pairing and superfluidity, caused by the continuumlattice mixing in 2DOL. We find that, in the presence of a finite population imbalance (p>0), the pair density at Tc unexpectedly approaches zero towards to deep BEC regime and thus the transition Tc is dramatically enhanced in the BEC regime and becomes proportional to the interaction strength $U$ in the BEC limit. This should be contrasted to the balanced case, for which Tc decreases as $1/U$. And the system is an intermediatetemperature polarized superfluid state at unitarity and in the BCS regime. We perform stability analysis, and present complete phase diagrams along with the behavior of superfuild density. We show that a stable polarized superfluid emerges at relatively high temperature. 
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