Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session D09: Quantum Phases in Optical LatticesLive

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Chair: Peter Schauss, University of Virginia Room: Portland 256 
Tuesday, June 2, 2020 2:00PM  2:12PM Live 
D09.00001: Conductivity of Ultracold Fermions in an Optical Lattice Peihang Xu, Vijin Venu, Rhys Anderson, Frank Corapi, Darby Bates, Cora J. Fujiwara, Frederic Chevy, Joseph H. Thywissen We discuss our recent measurements of the dynamics of global mass currents of ultracold $^{40}$K in a cubic optical lattice using a quantum gas microscope [1]. A periodic force is applied by sinusoidally displacing a harmonic optical potential. In the linear response regime, the ratio between current and force gives the conductivity, through Ohm's law. For various lattice depths, temperatures, interaction strengths, and fillings, we measure both the real and imaginary conductivity, up to a frequency sufficient to capture transport dynamics within the lowest band, and well below the band gap. The spectral width of the real conductivity reveals the current dissipation rate, and the integrated spectral weight is related to thermodynamic properties of the system through a sum rule. We observe that a finite lattice depth causes relaxation of current due to the breaking of Galilean invariance, which enables damping through collisions between fermions. We also discuss measurements in progress on applying this experimental technique to a strongly correlated regime of large onsite interactions, onedimensional systems, and disordered systems. \\ $^1$R. Anderson \textit{et al.}, Phys. Rev. Lett. {\bf 122}, 153602 (2019). [Preview Abstract] 
Tuesday, June 2, 2020 2:12PM  2:24PM Live 
D09.00002: Bilayer Fermi gas Microscope Thomas Hartke, Botond Oreg, Ningyuan Jia, Martin Zwierlein Quantum gases loaded into optical lattices with single site resolution have emerged as one of the most powerful quantum simulators for investigating exotic manybody physics related to condensed matter systems. Here, we demonstrate the ability to extract the full information of a singleband FermiHubbard model in the charge base without parity projection. By harnessing the power of Feshbach enhanced interactions between two atoms in a single well, we coherently load doubly occupied lattice sites into a doublewell trap, preventing light assisted atom loss during the imaging process. With the full charge occupation, we measure the compressibility of the cloud and show that the temperature can be measured from the densitydensity correlations according to a fluctuationdissipation theorem. Furthermore, we observe the strong correlation between doublons and holons, a signature of spinordering due to superexchange interactions. This work establishes the possibility to extract both the spin and charge information of a twocomponent Fermi gas, and provides a route to studying Hubbard physics beyond two dimensions by enabling transverse dynamics. [Preview Abstract] 
Tuesday, June 2, 2020 2:24PM  2:36PM Live 
D09.00003: Observing localisation in a 2D quasicrystalline optical lattice. JrChiun Yu, Matteo Sbroscia, Konrad Viebahn, Edward Carter, Ulrich Schneider Quasicrystals are longrange ordered but not periodic and represent an interesting middle ground between order and disorder. I will present how we experimentally realise a twodimensional quasicrystaline optical lattice for ultracold atoms with eightfold rotationally symmetric. [1] By studying the diverging timescale required for adiabatically loading, we probe the disorderinduced localised phase and demonstrate its resilience against to interactions. [2] Our experimental results are consistent with a meanfield shift of the localisation transition. Quasiperiodic potentials, lacking conventional rare regions, provide the ideal testing ground to realise manybody localisation in 2D. [1] Konrad Viebahn, Matteo Sbroscia, Edward Carter, JrChiun Yu, Ulrich Schneider. ``Matterwave diffraction from a quasicrystalline optical lattice''. Phys. Rev. Lett. 122, 110404 (2019). [2] Matteo Sbroscia, Konrad Viebahn, Edward Carter, JrChiun Yu, Alexander Gaunt, Ulrich Schneider. ``Observing localisation in a 2D quasicrystalline optical lattice''. arXiv:2001.10912 (2020). [Preview Abstract] 
Tuesday, June 2, 2020 2:36PM  2:48PM Live 
D09.00004: Evidence for unbounded growth of the number entropy in manybody localized phases Maximilian KieferEmmanouilidis, Razmik Unanyan, Michael Fleischhauer, Jesko Sirker In lattice systems with particlenumber conservation the von Neumann entanglement entropy $S_{\textrm{ent}}$ is the sum of number entropy $S_{\textrm{n}}$ and configurational entropy $S_\textrm{conf}$. As shown recently both quantities can be obtained in an experiment from the full counting statistics. We numerically investigate the particlenumber entropy $S_n$ following a quench in onedimensional interacting manybody systems with potential disorder. We find evidence that in the regime which is expected to be manybody localized and where the vonNeumann entanglement entropy is known to grow as $S_{\textrm{ent}}\sim \ln t$ as function of time $t$, also the number entropy increases as function of time as $S_n\sim\ln\ln t$. If this growth continues in the thermodynamic limit for infinite times, it would signal (ultraslow) ergodic behavior rather than localization of particles. We show furthermore that for free systems $S_{\textrm{ent}}$ is completely fixed by $S_{\textrm{n}}$. [Preview Abstract] 
Tuesday, June 2, 2020 2:48PM  3:00PM Live 
D09.00005: Exploring the Hofstadter spectrum with tunable bichromatic optical lattices Peter Dotti, Toshihiko Shimasaki, Shankari Rajagopal, David Weld We discuss experiments on quantum gases in tunable quasiperiodic optical potentials. Use of a bichromatic lattice with tunable period ratio between the two sublattices enables at least two new measurements. First, studying the frequencydependent response of a quasiperiodicallytrapped gas to lattice modulation offers a direct probe of the multifractal Hofstadter butterfly energy spectrum which also characterizes 2D electron gases in the integer quantum Hall regime. This extends previous experiments at fixed period ratio which have measured 1D slices of this 2D spectrum [1]. Second, observing time evolution of an initially narrow density distribution in a bichromatic lattice at rational and irrational period ratios allows a detailed probe of localization physics and may reveal signatures of a change in eigenvalue statistics across a localization transition. [Preview Abstract] 
Tuesday, June 2, 2020 3:00PM  3:12PM Live 
D09.00006: InteractionDriven Dynamics of a BoseEinstein Condensate in an Optical Lattice M. K. H. Ome, T. Bersano, S. Mossman, P. Engels, Q. Guan, D. Blume Ultracold clouds of atoms placed into carefully designed optical lattice potentials form an excellent tool for probing the dynamics of interacting, quantum mechanical particles. In this work, we investigate the properties of nonlinear Bloch bands of BoseEinstein condensates that come into existence for sufficiently strong interactions between the atoms. In our experiments, we analyze the properties of nonlinear Bloch bands by applying optical lattices and performing wellcontrolled lattice accelerations. The experiments reveal nonexponential tunneling of atoms which is conceptually connected to predicted loop structures. Our observation of nonexponential tunneling provides a clear demonstration of the power of ultracold atoms for investigating complex quantum mechanical dynamics. [Preview Abstract] 
Tuesday, June 2, 2020 3:12PM  3:24PM On Demand 
D09.00007: Critical superfluid velocity of spin1 bosons in an optical lattice Shion Yamashika, Ryosuke Yoshii, Shunji Tsuchiya We study the superfluid (SF)  Mott insulator (MI) transition of spin1 bosons with antiferromagnetic interaction in an optical lattice based on the spin1 BoseHubbard model [1]. It has been shown that in contrast to the spineless case the SFMI phase transition is of first order [2]. We derive the timedependent GinzburgLandau (TDGL) equation expanding up to the 6th order of the SF order parameter in the vicinity of the firstorder SFMI phase transition. We employ the TDGL equation to study the stability of superfluid mass current and spin current. Mass current induces dynamical instability involving the U(1) phase mode [3]. We find that the critical velocity of mass current is finite at the SFMI phase boundary due to the existence of the metastable SF state and it vanishes at the point where the metastable SF state disappears. Spin current also induces dynamical instability that involves spin wave excitations. We find a parameter region where the superfluid polar state is unstable against infinitesimal spin current. This implies emergence of an unknown magnetic phase in this parameter region that cannot be described by the meanfiled theory.\\ $^{1}$S.\,Tsuchiya, {\it et al.,} PRA {\bf 70}, 043628 (2004). \\ $^{2}$T.\,Kimura, {\it et al.,} PRL {\bf 84}, 110403 (2005). [Preview Abstract] 
Tuesday, June 2, 2020 3:24PM  3:36PM 
D09.00008: Topological Phases of Interacting Fermions in Optical Lattices Vito Scarola, Chuanchang Zeng, Tudor Stanescu, Chuanwei Zhang, Sumanta Tewari Recent experiments have placed cold atoms into optical lattices in the presence of synthetic fields. This talk will review studies of HubbardHofstadter models in regimes revealing topological phases of ultracold fermions arising from the interplay of interparticle interactions and synthetic fields in kagome and square optical lattices. Focusing on one regime in particular, attractive interactions in a square optical lattice, we find that attractive swave interactions lead to a higherorder topological superfluid [1]. Higherorder topological superconductors hosting MajoranaKramers pairs as corner modes have recently been proposed in twodimensional materials. Here, we show that such MajoranaKramers pairs can be realized using a conventional swave superfluid in an optical lattice but with a soliton. The MajoranaKramers pairs emerge at the “corners” defined by the intersections of line solitons and the onedimensional edges of the system. Our scheme sets the stage for observing possible higherorder topological superfluidity with conventional swave superfluids of cold atoms. 1. C. Zeng et al., Phys. Rev. Lett. 123, 060402 (2019) [Preview Abstract] 
Tuesday, June 2, 2020 3:36PM  3:48PM 
D09.00009: Experimental observation of nonergodic behavior in the tilted FermiHubbard model Thomas Kohlert, Sebastian Scherg, Bharath Hebbe Madhusudhana, Immanuel Bloch, Monika Aidelsburger Using ultracold fermionic $^{\mathrm{40}}$K atoms in an optical lattice we study the dynamics of the onedimensional FermiHubbard model subject to an external linear potential (``tilt''), which has recently attracted considerable theoretical and experimental interest in the context of ergodicitybreaking and constrained dynamics. Starting from a chargedensity wave initial state (quarter filling) we measure the spinresolved time evolution of the occupation imbalance between even and odd lattice sites as a local probe of localization. We identify two fundamentally different regimes: At short times we measure parityprojected realspace Bloch oscillations which, depending on the strength of the tilt, exhibit interaction induced damping and frequency modulation. At long times the dynamics reveal a robust steady state imbalance up to about 300 tunneling times, whose value depends on the interaction strength. We compare our experimental results to numerical calculations employing tDMRG on short time scales and exact diagonalization on long timescales and find excellent agreement throughout. Finally, we couple adjacent 1D systems to probe the crossover from a nonergodic 1D to an ergodic 2D system and find a spindependent decay of the imbalance depending on the transverse coupling strength. [Preview Abstract] 
Tuesday, June 2, 2020 3:48PM  4:00PM Not Participating 
D09.00010: Realization of BoseEinstein condensation in higher Bloch bands of an optical honeycomb lattice Tobias Klafka, Alexander Ilin, Julius Seeger, Phillip Gross, Klaus Sengstock, Juliette Simonet BoseEinstein condensates in higher Bloch bands of optical lattices immensely extend the possibilities for quantum simulation of solid state models. Unconventional superfluids and new topological states of matter are expected to emerge from the interplay of spin and orbital degrees of freedom as well as the lattice symmetry. We report on BoseEinstein condensation in the second and fourth band of a bipartite honeycomb lattice. Tuning the energy offset between the two sublattices allows a controlled transfer to higher bands. We have investigated the emergence of coherence for these metastable states as well as the interplay of band relaxation dynamics and condensation by tracing the dynamics in the Brillouin zones. Understanding these nonequilibrium processes constitutes an essential requirement for the stabilization of unconventional spinor condensates in higher bands. [Preview Abstract] 
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