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 K09: Degenerate Fermi Gas IIRecordings Available

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Chair: Joseph Thywissen, Toronto Room: Salon 11/12 
Wednesday, June 1, 2022 10:30AM  10:42AM 
K09.00001: A multipurpose quantum simulation setup with Lithium 6 atoms. Joris Verstraten, Kunlun Dai, Shuwei Jin, Christophe Salomon, Bruno Peaudecerf, Tarik Yefsah Quantum science has become an extremely active area of research, relying on physical realizations of large and wellcontrolled quantum systems. With quantum gases of ultracold atoms, experiments have had tremendous success in tackling quantum manybody problems, which are notoriously challenging, thanks to their capabilities to create quantum systems with incremental complexity. However, a limitation of the current approaches is that, typically, each quantum gas experiment is optimized to address a certain type of problems. One often has to choose between lattice or continuous systems, short or longrange interactions, singleparticle detection or bulk measurements, etc. In this talk, we will present a design for a 6Libased quantum gas platform that aims to provide wideranging capabilities, where one could address a variety of quantum problems that have historically been treated on different setups. The use of 6Li makes the setup suitable for the study of BECBCS physics, Fermi Hubbard Physics and Rydberg systems, while the architecture is compatible with a quantum gas microscope and tailored optical potentials. This twochamber setup relies on robust and easy to implement techniques, allowing to produce low entropy ensembles of fermions with temperatures and atom numbers that are compatible with a wide range of manybody problems. 
Wednesday, June 1, 2022 10:42AM  10:54AM 
K09.00002: Thermalization dynamics of a dissipative twolevel system in a Fermi bath with contact interactions Franklin J Vivanco, Alexander Schuckert, Grant Schumacher, Yunpeng Ji, Gabriel Assumpcao, Jianyi Chen, Michael Knap, Nir Navon We study the dynamics of a quasihomogeneous Fermi gas under a strong internalstate drive. A highly spinimbalanced weaklyinteracting mixture is created in two internal states in a box trap. The minority is then driven to a third internal state with a radiofrequency field, where this third state interacts via unitary limited interactions with the majority. We investigate the dynamics of the minority under a strong drive with a Rabi frequency much larger than the Fermi energy of the host atoms. We extract the Rabi frequency renormalized by interactions and the relaxation of the effective magnetization (the relative population difference). We observe that after a few cycles, the system reaches a nontrivial steady state characterized by a detuningdependent magnetization. This system is understood as dissipative twolevel systems, which evolve to their thermal equilibrium state via interactions with the fermionic bath. We extract the effective T1 and T2 times characterizing the decay to the steadystate as well as the meanfield shift of the resonance frequency of the twolevel systems. Our study paves the way to studying equilibrium states of unitary Fermi gases in the presence of strong driving fields. 
Wednesday, June 1, 2022 10:54AM  11:06AM 
K09.00003: Fermi Polaron lifetimes at finite momentum from a functionalrenormalizationgroup approach Jonas von Milczewski, Aileen Durst, Richard Schmidt We study theoretically the lifetimes of the attractive and the repulsive Fermi Polaron and the molecule at finite momentum in both two and three dimensions. To this end, we developed a new technique that allows for the computation of Green's functions in the whole complex frequency plane using exact analytical continuation within the functional renormalization group. While conventional approaches like the NSCT method cannot determine these lifetimes, we are able to find the momentum dependent lifetime at different interaction strengths of both the attractive and repulsive polaron as well as the molecule. In our talk we discuss our findings and talk about possible experiments which could be conducted. 
Wednesday, June 1, 2022 11:06AM  11:18AM 
K09.00004: Hydrodynamic Relaxation in a Strongly Interacting Fermi Gas Xin Wang, Xiang Li, Ilya Arakelyan, John E Thomas We report new timedomain, free evolution methods for measuring hydrodynamic transport coefficients in a strongly interacting Fermi gas. We measure the free decay of a spatially periodic density profile in a twostate mixture of ^{6}Li in the normal fluid phase, confined in a box potential. This spatial profile is initially created in thermal equilibrium by a perturbing potential. After the perturbation is abruptly extinguished, the dominant spatial Fourier component exhibits an exponentially decaying (thermally diffusive) mode and a decaying oscillatory (first sound) mode, enabling independent measurement of the thermal conductivity and the shear viscosity directly. 
Wednesday, June 1, 2022 11:18AM  11:30AM 
K09.00005: Persistent current decay in an atomic ring trap Klejdja Xhani, Giulia Del Pace, Woo Jin Kwon, Alessandro Muzi Falconi, Marco Fedrizzi, Nicola Grani, Diego Hernandez Rajkov, Francesco Scazza, Giacomo Roati The motion of quantized vortices is of fundamental importance in different phenomena in condensed matter physics such as the resistive behaviour of superconductors or many other dissipative collective phenomena in superfluids. In particular, here we investigate theoretically their role on the decay of persistent current in ringshaped atomic superfluids and in the presence of a small defect. In our studies, we model a recent experiment of ^{6}Li at LENS in the limit of BoseEinstein condensate of molecules. The numerical simulations are performed at T=0 by solving the GrossPitaevskii equation. A finite circulation state is excited by imprinting a phase in the equilibrium condensate wavefunction. In the absence of the defect, the current is persistent and the superflow is dissipatonless up to a maximum circulation. When a small defect instead is introduced, there is a critical velocity, i.e. a critical circulation, at which the vortices are emitted into the superfluid causing phase slips and thus a transition of the quantized initial circulation states to lower values (i.e. a decay of the current in time). We then give a microscopic description of such mechanism and its dependence on defect parameters and circulation state. 
Wednesday, June 1, 2022 11:30AM  11:42AM 
K09.00006: On the Stability of the Repulsive Fermi Gas with ShortRange Interactions Yunpeng Ji, Gabriel Assumpção, Jianyi Chen, Jere Mäkinen, Grant Schumacher, Philip Tuckman, Franklin Vivanco, Nir Navon We study the stability of a homogeneous spin1/2 Fermi gas with repulsive shortrange interactions. This manybody repulsive 'branch' is metastable towards the formation of Feshbach bound states, via threebody recombination. We measure the universal recombination coefficient $K_3$ and observe universal scalings with the average kinetic energy per particle and twobody scattering length. The scaling exponents are in excellent agreement with the linear energy dependence arising from a threebody threshold law involving two indistinguishable fermions and the $a^{6}$ scaling for threebody collisions in twocomponent Fermi gas under zerorange approximation. The interplay of the momentum dependence of the recombination coefficient and the Fermi statistics leads to nontrivial temperature dynamics, alternatively heating or cooling depending on the initial quantum degeneracy. The universal scaling with interactions extends over four orders of magnitude and beyond the expected range of validity of the threebody recombination law. 
Wednesday, June 1, 2022 11:42AM  11:54AM 
K09.00007: Stability of quantum degenerate fermionic polar molecules without and with microwave shielding Axel Pelster, Antun Balaz A stabilization of a fermionic molecular gas towards collapse in attractive headtotail collisions and its evaporative cooling below the Fermi temperature has so far been achieved in two ways. Either a strong dc electric field is applied to confine the molecular motion to 2D [1] or inelastic collisions in 3D are strongly suppressed by applying a circularly polarized microwave field [2]. Here we use a HartreeFock meanfield theory [3,4] in order to determine the 3D properties of quantum degenerate fermionic molecules. In particular, we compare the stability diagrams occurring without (with) microwave shielding, where a (negative) dipoledipole interaction is present. In case that the orientation of the electric dipoles with respect to the trap axes is unknown, we outline how to reconstruct it from timeofflight absorption measurements. 
Wednesday, June 1, 2022 11:54AM  12:06PM 
K09.00008: Density fluctuations in three & twodimensional SU(N) Fermi gases Chengdong HE, Entong ZHAO, Ka Kwan Pak, Yujun Liu, GyuBoong Jo For a degenerate SU(N) Fermi gas, spin multiplicity N affects its thermodynamics and quantum fluctuations, especially in the deep degenerate regime. Although a lot of efforts have been put in investigating intriguing properties of SU(N) Fermi gases, the thermodynamics of imbalanced high spin system remains unexplored. 
Wednesday, June 1, 2022 12:06PM  12:18PM 
K09.00009: Observation of superfluid current through a dissipative quantum point contact Jeffrey Mohan, Philipp Fabritius, AnneMaria Visuri, Mohsen Talebi, Simon Wili, Shun Uchino, Thierry Giamarchi, MengZi Huang, Tilman Esslinger We experimentally and theoretically confirm the robustness of fermionic superfluidity to spindependent particle dissipation in a unitary Fermi gas. By locally illuminating a quantum point contact connecting two superfluid reservoirs with a beam resonant with one of the two spin states, we engineer particle loss and measure its effect on the signature of superfluidity in our system: a nonOhmic supercurrent carried by multiple Andreev reflections (MAR). We develop a meanfield model in the Keldysh formalism that quantitatively reproduces our observations. We find that there is no critical dissipation strength where the supercurrent vanishes. Instead, it smoothly decays towards zero with increasing dissipation, indicating a surprising robustness of MAR. Our model also predicts that Onsager's reciprocal relations are violated due to broken detailed balance, which we hope to soon experimentally confirm as it can have significant implications for dissipative engineering of transport properties. 
Wednesday, June 1, 2022 12:18PM  12:30PM 
K09.00010: A new experimental apparatus for exploring the SU(N) FermiHubbard model Jonatan Höschele, Sandra Buob, Antonio RubioAbadal, Vasiliy Makhalov, Leticia Tarruell The FermiHubbard model is a cornerstone model of condensed matter physics. Extending this model to the SU(N) symmetric case promises new exotic magnetic phases beyond the limits of natural materials. The behavior of such systems is hard to predict theoretically. Experimentally however, the SU(N) FermiHubbard model can be realized and studied with the fermionic isotopes of alkalineearth atoms, where the interactions are SU(N) symmetric, i.e., independent of the internal state of the atom. In our experiment, we use ultracold fermionic strontium atoms which have with N = 10 the largest SU(N) symmetry available to atomic physics. Making use of the narrow red transition of strontium, we reach few μK temperatures, enabling direct loading into an optical dipole trap for further evaporative cooling. Once we reach quantum degeneracy, we plan to load the strontium atoms into an optical lattice, operating at a magic wavelength. To probe the system, e.g., its ground state, we will install a highNA objective, enabling us to image with single atom and single site resolution. Making use of the clock transition to spindependently shelve the atoms in the clock state, we will also be able to extract the spin structure of the system. In my talk I will present the design of the machine and the current status of the experiment. 
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