Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session B28: Quantum Gases in Optical LatticesLive

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Sponsoring Units: DAMOP Chair: Han Pu, Rice Univ 
Monday, March 15, 2021 11:30AM  11:42AM Live 
B28.00001: A Computational Study of Dynamical Properties of Cold Atomic Fermi Systems: Trapped Gases and Systems Moving on Optical Lattices Patrick Kelly We present preliminary results of a study of a cold atomic Fermi gas in a few relevant density regimes, addressing trapped dilute gases and gases embedded in optical lattices, modeled with a Hubbard Model Hamiltonian. This work builds on our previous research on the supersolid phase, which arises in a twodimensional Fermi gas at halffilling, spinbalanced, on an optical lattice. Researchers in many areas of physics are interested in cold atoms because of their potential to serve as physical models of seemingly unrelated systems, such as superconductors and the superfluid interiors of neutron stars. Leveraging quantum Monte Carlo (QMC) simulations and cuttingedge analytic continuation techniques we can obtain unbiased results for static and dynamical correlation functions. We also apply Generalized Random Phase Approximation (GRPA) in our investigation. QMC, unlike GRPA, gives exact results. However, GRPA allows for much finer resolution in the momentum domain when calculating dynamical correlation functions. Consequently, the strengths of one method make up for the potential weaknesses in the other. Taken together, these methodologies provide an excellent set of tools for studying the exotic and counterintuitive properties of cold atomic gases. 
Monday, March 15, 2021 11:42AM  11:54AM Live 
B28.00002: Competing scenarios for dipolar hardcore bosons within square and triangular lattices WeiLin Tu, HuanKuang Wu, Takafumi Suzuki, Hyunyong Lee, Naoki Kawashima Thanks to the fast development of coldatom experiments, an exotic quantum phase with coexisting solid(diagonal) and superfluid(offdiagonal) longrange orders, also named after the supersolid state, has been realized. This quantum phase was discovered within a trapped BoseEinstein condensate made of dipolar atomic gases. Within a planer lattice, such dipolar interaction can be easily tuned by varying the external field, and thus remains flexible for creating distinct scenarios. In our recent works, we have found a competing scenario between phases belonging to different lattice symmetry, among the variation of dipolar angles. Based on the preliminary meanfield analysis, we further made use of numerical techniques and provided more insightful features of the phase diagrams. Experimentally, we believe that the tuning of dipolar interaction helps change the geometrical structure of the lattice and realize an effective reciprocal structure. 
Monday, March 15, 2021 11:54AM  12:06PM Live 
B28.00003: Contrasting lattice geometry dependent versus independent quantities and applications to cold atom experiments. Steven Simon, Mark Rudner The ability to create and manipulate optical lattices for cold atoms, with a view towards studying topological matter, has brought renewed focus to the physics of Bloch waves and the role of the lattice in governing their properties. We consider generic tight binding models where particle motion is described in terms of hopping amplitudes between orbitals. The physical attributes of the orbitals, including their locations in space, are independent pieces of information. We identify a notion of geometryindependence: any physical quantity that depends only on the tightbinding parameters (and not on the explicit information about the orbital geometry) is said to be "geometryindependent." Identification of geometrydependent vs. independent quantities can be used as a novel principle for constraining a variety of results in both noninteracting and interacting systems. We show, e.g., how Hall measurements based on accelerated lattices or tilted potentials, and those based on applying a chemical potential imbalance between reservoirs, give different results due to the fact that one is geometrydependent, while the other is geometryindependent. Similar considerations apply for thermal Hall responses in electronic, cold atomic, and spin systems. 
Monday, March 15, 2021 12:06PM  12:18PM Live 
B28.00004: Critical opalescence across the dopingdriven Mott transition in the twodimensional fermionic Hubbard model Giovanni Sordi, Caitlin Walsh, patrick Sémon, AndreMarie Tremblay Phase transitions and their associated crossovers are imprinted in the behavior of fluctuations. Motivated by recent experiments on cold atoms in optical lattices, we study the thermodynamic density fluctuations δN^{2 }of the 2D Hubbard model with plaquette cellular dynamical meanfield theory. To understand the length scale of these fluctuations, we separate the local from the nonlocal contributions to δN^{2}. We determine the effects of particle statistics, interaction strength, temperature, and density. At high temperature, our theoretical framework reproduces the experimental observations in the dopingdriven crossover regime between metal and Mott insulator. At low temperature, there is an increase of thermodynamic density fluctuations, analogous to critical opalescence, accompanied by a reduction of the absolute value of their nonlocal contributions. An enhancement in the energy fluctuations is also found. This is a precursory sign of an underlying transition between a pseudogap phase and a metallic phase in doped Mott insulators, which could play a key role in cuprates. We propose predictions for cold atom experiments. 
Monday, March 15, 2021 12:18PM  12:30PM Live 
B28.00005: Phase diagram of SU(3) Fermi gases with population imbalance in square optical lattices Hayato Motegi, Daisuke Yamamoto, Giacomo Marmorini, Nobuo Furukawa Ultracold alkalineearth(like) atoms in optical lattices represent an ideal platform to study SU(N) magnetism. Recently, shortrange SU(N > 2) magnetic correlations have been observed in ^{173}Yb systems [1,2]. Here we focus on the magnetic orderings in threecomponent SU(3) Fermi gases loaded into a square optical lattice. Previous studies have suggested that the ground state of the equally populated system has a threesublattice stripe order [3]. We consider the case with population imbalance between one component and the others. In general, reducing the symmetry with population imbalance is expected to lead to exotic orders and phase transition phenomena [4]. We discuss the lowtemperature properties and the thermal phase transition phenomena using the linear flavorwave theory and semiclassical Monte Carlo method, respectively. Several magnetic states arise from the competition between antiferromagnetic interactions and population imbalance, including a peculiar partiallydisordered state with checkerboard longrange order. 
Monday, March 15, 2021 12:30PM  12:42PM Live 
B28.00006: Higherorder correlations in the FermiHubbard model Annabelle Bohrdt, Joannis Koepsell, Dominik Bourgund, Pimonpan Sompet, Sarah Hirthe, Yao Wang, Marton KanaszNagy, Guillaume Salomon, Christian Gross, Immanuel Felix Bloch, Eugene Demler, Fabian Grusdt Traditionally, one and twopoint correlation functions are used to characterize manybody systems. 
Monday, March 15, 2021 12:42PM  12:54PM Live 
B28.00007: SU($N$) alkalineearth fermions in optical lattices: thermodynamics and magnetism. Eduardo Ibarra Garcia Padilla, HaoTian Wei, Shintaro Taie, Naoki Nishizawa, Yosuke Takasu, Yoshihito Kuno, Yoshiro Takahashi, Richard Theodore Scalettar, Kaden Hazzard Our recent observation of nearestneighbor antiferromagnetic (AFM) spincorrelations in an SU(6) $^{173}$Yb Fermi gas loaded in 1D, 2D, and 3D optical lattices, opens new questions about strongly correlated systems\footnote{S. Taie, et. al., arXiv:2010.07730}. Two major questions are how longrange correlations form, and what happens when the system is doped away from the Mott insulating regime. We report progress towards answering these questions. In our previous work, we calculated the experimentally measured properties and found that the nearestneighbor AFM correlations agree quantitatively with no fitting for all temperatures in 1D, and at temperatures where converged theoretical results can be obtained in 3D. In 1D, experiments reached the lowest $k_BT/t$ ever reported for a Fermi gas in an optical lattice. These results lay the foundation for our ongoing studies of longranged magnetism and doped Mott insulators. We numerically study the thermodynamics and magnetism of the SU($N$) Fermi Hubbard as a function of $N$, $U$, and $T$ in 2D at unitfilling using determinant Quantum Monte Carlo. Our results are experimentally relevant, since experiments are now poised to discriminate finite temperature analogs of theoretically proposed ground states using quantum gas microscopy. 
Monday, March 15, 2021 12:54PM  1:06PM 
B28.00008: Observation of dynamical manybody quantum phase transitions beyond KibbleZurek mechanism Qi Huang, Ruixiao Yao, Shuai Wang, Dingping Li, Wenlan Chen, Xuzong Chen, Jiazhong Hu The quantum critical behaviors of manybody phase transition is one of the most fascinating but also challenging questions in quantum physics. Here, we develop an improved bandmapping method, and investigate the dynamical quantum phase transition from a superfluid to a Mott insulator. We observe the quantum critical behaviors deviate from a universal powerlaw scaling description which is known as the KibbleZurek mechanism. There is an asymmetric quantum critical behavior around the critical point that there are a rapid response in the superfluid regime and a much retarded or even failed relaxation in the Mott insulator side. The response time and the excitation fraction in Mott insulators are dominated by two different powerlaw scaling which is inconsistent with the universality of quantum criticality. This shows that there may be complex mechanism competitions in manybody quantum phase transition which cannot be simply captured by the conventional KibbleZurek Mechanism. 
Monday, March 15, 2021 1:06PM  1:18PM Live 
B28.00009: Phase and group velocities for correlation spreading in the Mott phase of the BoseHubbard model in dimensions greater than one Ali MokhtariJazi, Matthew Ronald Charles Fitzpatrick, Malcolm Kennett LiebRobinson and related bounds set upper limits on the rate at which information propagates in nonrelativistic quantum systems. Experimentally, they have been observed in the spreading of correlations in the BoseHubbard model (BHM) after a quantum quench. Using a two particle irreducible (2PI) strong coupling approach to outofequilibrium dynamics in the BHM we calculate both the group and phase velocities for the spreading of singleparticle correlations in 1, 2 and 3 dimensions as a function of interaction strength. Our results are in quantitative agreement with measurements of the velocities for the spreading of single particle correlations in both the 1 and 2 dimensional BHM realized with ultracold atoms. They also agree with the claim that the phase velocity rather than the group velocity was observed in recent experiments in 2 dimensions. We demonstrate that there can be large differences between the phase and group velocities for the spreading of correlations and explore the variation of the anisotropy in the velocity at which correlations spread across the phase diagram of the BHM. Our results establish the 2PI strong coupling approach as a powerful tool to study outofequilibrium dynamics in the BHM in dimensions greater than 1. 
Monday, March 15, 2021 1:18PM  1:30PM Live 
B28.00010: Ferromagnetism in ddimensional SU(n) Hubbard models with nearly flat bands Kensuke Tamura, Hosho Katsura The SU(n) Hubbard model, which describes multicomponent fermions with SU(n) symmetric interaction, has attracted much attention recently because of its realization in coldatom setups[1]. However, there are few rigorous results established for this model with n>2. 
Monday, March 15, 2021 1:30PM  1:42PM Live 
B28.00011: Effects of densityinduced hopping on tilted dipolar bosons in a square lattice Barbara CapogrossoSansone, Chao Zhang, Jin Zhang, Jin Yang Motivated by recent experiments with ultracold magnetic atoms trapped in optical lattices where the orientation of atomic dipoles can be fully controlled by external fields, we study the ground state properties of dipolar bosons trapped in a twodimensional lattice with densityinduced hopping and where the dipoles are tilted along the xz plane. We present ground state phase diagrams of the above system at different tilt angles. We find that, as the dipolar interaction increases, the superfluid phase at half filling factor is destroyed in favor of either a checkerboard or stripe solid phase for tilt angle θ< 35.3^{o} or θ > 35.3^{o} respectively. More interesting physics happens at tilt angles θ>58^{o} where we find that, as the dipolar interaction strength increases, solid phases first appear at filling factor lower than 0.5. Moreover, unlike what observed at lower tilt angles, we find that, at half filling, the superfluid gives way to a stripe solid through a stripe supersolid phase. 
Monday, March 15, 2021 1:42PM  1:54PM Live 
B28.00012: Probing quantum phases and the Hall response in bosonic flux ladders Maximilian Buser, Sebastian Greschner, Claudius Hubig, Leticia Tarruell, Fabian HeidrichMeisner, Thierry Giamarchi, Ulrich Joseph Schollwoeck The focus of this talk is on bosonic flux ladders. First, we touch on a model which is envisioned to be realized in a future quantum gas experiment exploiting the internal states of potassium atoms as a synthetic dimension. Considering specifics of the future experiment, we map out the groundstate phase diagram and report on Meissner and biasedladder phases. We show that quantum quenches of suitably chosen initial states can be used to probe the equilibrium properties of the dominant groundstate phases. 
Monday, March 15, 2021 1:54PM  2:06PM On Demand 
B28.00013: Semiclassical analysis of frustrated Bose gases in optical kagome lattices Yusuke Ozaki, Daisuke Yamamoto, Ippei Danshita Frustration, which causes extensive degeneracy near the ground state of a manybody system, has received considerable interest because it is an essential component for understanding the various emergent phenomena in manybody systems [1]. Specifically, in the case of noninteracting particles on a kagome lattice, a flat band appears as a clear feature of the frustration. 
Monday, March 15, 2021 2:06PM  2:18PM On Demand 
B28.00014: Analysis of shape change of droplet in dipolar BoseHubbard model Kazuhiro Tamura, Shohei Watabe, Tetsuro Nikuni Peculiar phenomena, such as supersolids, in BoseEinstein condensates (BECs) emerge from dipolar interaction. The longrange and anisotropic nature of the dipolar interaction provides superfluid phase and stripe or checkerboard supersolid phases in BECs in an optical lattice. On the other hand, BECs could be unstable in a certain area of dipole interaction parameters. In this presentation, in order to qualitatively understand droplet formations in this unstable regime, we propose a toy model that allows us to estimate size and shape of droplets in dipolar BoseHubbard system in an optical lattice. We compare the results of the toy model with the numerical solution of the meanfield calculation. 
Monday, March 15, 2021 2:18PM  2:30PM On Demand 
B28.00015: Propagation of dark soliton from superfluid core to Mottinsulator shell and superfluid shell Yuma Watanabe, Shohei Watabe, Tetsuro Nikuni We study dynamics of phase imprinted solitons of ultracold bosons in an optical lattice with a harmonic trap, which shows the superfluid (SF) and Mottinsulator (MI) shell structures. In the uniform BoseHubbard system, he soliton generated by the phase imprinting method is known to propagate in three different ways in the uniform system [Konstantin V. Krutitsky, Phys. Rev. A 82, 033618 (2010).], such as the inphase soliton, outofphase soliton, and wavelet. In this presentation, we discuss the propagation of phase imprinting soliton from the inner superfluid core to Mottinsulator shell and outer superfluid shell. All the three types of solitonic excitations are deformed into an inphase soliton before the excitation irrupts into the Mott shell, because of the spatial dependence of the effective chemical potential. Interestingly, in the inphase soliton and outofphase soliton regimes, the excitation does not penetrate into the outer SF shell, and is reflected by its surface. By inducing a repulsive potential at the center of the trap, however, we can inject the wavelet to the MI shell, and permeate the excitation into the outer SF shell. 
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