Bulletin of the American Physical Society
53rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 67, Number 7
Monday–Friday, May 30–June 3 2022; Orlando, Florida
Session U09: Gauge Fields and SpinOrbit CouplingRecordings Available

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Chair: Richard Fletcher, MIT Room: Salon 11/12 
Thursday, June 2, 2022 2:00PM  2:12PM 
U09.00001: Orbital order and chiral currents of interacting bosons with πflux Nathan Goldman, Marco Fedele F Di Liberto Higher Bloch bands provide a remarkable setting for realizing manybody states that spontaneously break timereversal symmetry, offering a promising path towards the realization of interacting topological phases. Here, we propose a different approach by which chiral orbital order effectively emerges in the lowenergy physics of interacting bosons moving on a square plaquette pierced by a πflux. We analyze the lowenergy excitations of the condensate in terms of two orbital degrees of freedom and identify a gapped collective mode corresponding to the outofphase oscillations of the relative density and phase of the two orbitals. We further highlight the chiral nature of the ground state by revealing the cyclotronlike dynamics of the density upon quenching an impurity potential on a single site. Our singleplaquette results can be used as building blocks for extended dimerized lattices, as we exemplify using the BBH model of higherorder topological insulators. Our results provide a distinct direction to realize interacting orbitallike models with broken timereversal symmetry, without resorting to higher bands nor to external drives, with direct implications for cold gases and nonlinear photonics. 
Thursday, June 2, 2022 2:12PM  2:24PM 
U09.00002: Crystallization of bosonic quantum Hall states Airlia Shaffer, Biswaroop Mukherjee, Parth B Patel, Zhenjie Yan, Cedric Wilson, Valentin Crepel, Richard Fletcher, Martin W Zwierlein The dominance of interactions over kinetic energy lies at the heart of strongly correlated quantum matter, from fractional quantum Hall liquids, to atoms in optical lattices and twisted bilayer graphene. Crystalline phases often compete with correlated quantum liquids, and transitions between them occur when the energy cost of forming a density wave approaches zero. A prime example occurs for electrons in highstrength magnetic fields, where the instability of quantum Hall liquids towards a Wigner crystal is heralded by a rotonlike softening of density modulations at the magnetic length. Remarkably, interacting bosons in a gauge field are also expected to form analogous liquid and crystalline states. However, combining interactions with strong synthetic magnetic fields has been a challenge for experiments on bosonic quantum gases. Here we study the purely interactiondriven dynamics of a Landau gauge Bose–Einstein condensate in and near the lowest Landau level. We observe a spontaneous crystallization driven by condensation of magnetorotons, excitations visible as density modulations at the magnetic length. Increasing the cloud density smoothly connects this behaviour to a quantum version of the Kelvin–Helmholtz hydrodynamic instability, driven by the sheared internal flow profile of the rapidly rotating condensate. At long times the condensate selforganizes into a persistent array of droplets separated by vortex streets, which are stabilized by a balance of interactions and effective magnetic forces. 
Thursday, June 2, 2022 2:24PM  2:36PM 
U09.00003: Engineering a Fractional Quantum Hall State of Bosons in an Optical Lattice Sooshin Kim, Julian Léonard, Joyce Kwan, Perrin C Segura, Markus Greiner Realization of strongly interacting particles under the presence of a magnetic field can lead to novel phases of matter with topological order. Here, we demonstrate adiabatic preparation of the ground state of a twoparticle HarperHofstadter system under different fluxes with ultracold bosonic ^{87}Rb atoms in an optical lattice. A superimposed running lattice of two Raman beams and a magnetic field gradient are utilized to apply a tunable synthetic gauge field on the atoms. With the singlesite resolution provided by our quantum gas microscope, we explore the groundstate fidelity of our protocol over the space of multiple parameters. There are more observables being studied to exhibit phase transition into the fractional quantum Hall state. Our study presents characterization of passage towards topological states in opticallattice experiments. 
Thursday, June 2, 2022 2:36PM  2:48PM 
U09.00004: Geometric squeezing of a degenerate Fermi gas Cedric Wilson, Airlia Shaffer, Parth B Patel, Zhenjie Yan, Biswaroop Mukherjee, Richard Fletcher, Martin W Zwierlein We report on the realization of a geometrically squeezed state of a rapidly rotating atomic Fermi gas and the measurement of its Hall response. A rotating, elliptical harmonic trap realizes the squeezing Hamiltonian for guiding center motion. The Fermi gas thus shrinks down in one direction to a size limited, via Pauli exclusion, to the width of the highest occupied cyclotron mode. In the orthogonal direction it expands exponentially, at a local speed given by the local Hall drift velocity, analogous to the $\vec{E} \times \vec{B}$ drift of charged particles in crossed electric and magnetic fields. Our work paves the way towards studying quantum Hall physics with atomic Fermi gases. 
Thursday, June 2, 2022 2:48PM  3:00PM 
U09.00005: Measurement of Excitations in the Stripe Phase of a SpinOrbit Coupled BoseEinstein Condensate Md Kamrul Hoque Ome, Annesh Mukhopadhyay, Sean Mossman, Xiwang Luo, Chuanwei Zhang, Peter W Engels Recent experimental progress with quantum gases is providing new avenues for the study of exotic stripe phases and supersolidlike properties from a variety of different perspectives. In our lab, we generate a superfluid stripe phase by combining Raman induced spinorbit coupling with an additional weak optical lattice. We study the excitation spectrum by applying Raman detuning quenches and observing the resulting spin polarization. We characterize the zeromomentum bandgap as a function of the optical lattice coupling strength and find good agreement between the experimental observations and numerical simulations. This work provides a direct experimental confirmation of the gapped pseudoGoldstone spectrum and opens the door for further investigations into the excitation dynamics of a superfluid stripe phase. 
Thursday, June 2, 2022 3:00PM  3:12PM 
U09.00006: Interacting spinorbit coupled fermions in a WannierStark optical lattice clock Anjun Chu, Alexander Aeppli, Tobias Bothwell, Colin J Kennedy, Dhruv Kedar, Peiru He, Ana Maria Rey, Jun Ye We theoretically analyze the interactions between driven spinorbit coupled fermions in an optical lattice clock based on the partially delocalized WannierStark states in a gravitytilted shallow lattice. We derive a manybody spin model and consider the following two cases: In carrier transition, we show that the relative strength of the onsite pwave interactions and offsite swave interactions can be easily tuned by lattice intensity, which allows us to precisely cancel the density shift at a "magic" lattice depth; In offsite WannierStark transitions, the swave interaction can be significantly enhanced, providing an ideal platform for realizing a ferromagnetic to paramagnetic dynamical phase transition. Our predictions have been demonstrated by recent experimental observations in an optical lattice clock with record clock precision. 
Thursday, June 2, 2022 3:12PM  3:24PM 
U09.00007: Engineering manybody interactions in a spinorbitcoupled WannierStark optical lattice clock Alexander G Aeppli, Anjun Chu, Tobias Bothwell, Colin J Kennedy, Dhruv Kedar, Peiru He, Kyungtae Kim, Ana Maria Rey, Jun Ye We present recent experimental work towards understanding and harnessing atomic interactions within a strontium optical lattice clock [1]. Our vertically oriented, shallow, 1D optical lattice realizes partially delocalized WannierStark eigenstates with superior quantum coherence [2]. On a single site, fermionic Sr atoms interact via weak pwave interactions. Due to incommensurate lattice and clock wavelengths, spinorbit coupling allows atoms in neighboring sites to interact via the swave channel. Balancing these collisional shifts, we can operate our optical lattice clock with a far higher onsite density while realizing a negligible density shift. Interactions are enhanced by addressing a sitechanging WannierStark transition. With the swave channel effectively opened to onsite interactions, the collisional shift is far greater in magnitude. We utilize this technique along with in situ imaging to observe a dynamical phase transition between dynamical ferromagnetic and paramagnetic states. 
Thursday, June 2, 2022 3:24PM  3:36PM 
U09.00008: SelfSpinning Crystallized Rotating BoseEinstein Condensates Ruixiao Yao, Airlia Shaffer, Cedric Wilson, Biswaroop Mukherjee, Parth B Patel, Zhenjie Yan, Richard Fletcher, Martin W Zwierlein The dynamics of interacting BoseEinstein Condensates (BEC) coupled to artificial gauge fields remains a crucial question for understanding exotic quantum phenomenon like the quantum Hall effect and typeII superconductivity. Under extreme rotation and weak interactions, a Landau gauge BEC will spontaneously crystallize into a persistent array of droplets, due to the balance between effective magnetic forces and interactions^{1}. Here we study the longtime dynamics of these condensed droplets. We find that in the rotating frame the droplets are spinning at a constant frequency. In Lowest Landau Level (LLL), the rate of rotation continously increases from zero upon turning on interaction. While in ThomasFermi regime, when multiple Landau levels are occupied, the rotation speed saturates to a particular fraction of cyclotron frequency. Our results provide a novel realization of time crystals and flatband localization. 
Thursday, June 2, 2022 3:36PM  3:48PM Withdrawn 
U09.00009: Stripe phase in a spinorbit coupled BoseEinstein condensate with attractive interstate interactions Craig S Chisholm, Ramon Ramos, Leticia Tarruell Supersolids are an exotic phase of matter combining the contrasting characteristics of rigidity in crystalline solids and frictionless flow in superfluids. In spinorbit coupled BoseEinstein condensates, the double minimum structure of the dispersion at small coupling enables the existence of a supersolidlike stripe phase. The stability of the stripe phase is limited by the miscibility of the components of the spinorbit coupled system. We present a scheme to exploit highly tunable interactions in potassium39 to enter a highly stable stripe phase with attractive interstate interactions. The characteristic density modulation can be imaged directly using matterwave optics. Furthermore, we investigate the effect of highly imbalanced intrastate interactions on the phase diagram and the excitation spectrum of the system. 
Thursday, June 2, 2022 3:48PM  4:00PM 
U09.00010: Collective excitations of BoseEinstein condensate in a synthetic magnetic field Yifan Du, Chunlei Qu The realization of synthetic magnetic field offers a new opportunity for the study of topological phenomena with ultracold neutral atoms. Synthetic magnetic field can also strongly modify the superfluid properties of a BoseEinstein condensate by generating a rotational velocity field and creating vortices. We explore the collective excitations in a spinorbitcoupled BoseEinstein condensate in the presence of a positiondependent detuning or Raman coupling. We find that various collective modes such as the scissors mode, the quadrupole mode, and the dipole mode can be coupled together due to the rotational velocity field. We have developed a hydrodynamic theory for the description of the collective excitations in both the singleminimum phase and the planewave phase. Our theoretical results are also compared to the numerical simulation of the GrossPitaevskii equation. 
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