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 E05: Degenerate Fermi Gas IRecordings Available

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Chair: Sruthi Venkataramanababu, Northwestern University Room: Salon 9/10 
Tuesday, May 31, 2022 2:30PM  2:42PM 
E05.00001: Pauli blocking enhanced lifetimes and cooperative radiation in a 2D Fermi gas Thomas Bilitewski, Ana Maria Rey, Jun Ye, Asier Pineiro Orioli, Christian Sanner, Lindsay Sonderhouse, Ross Hutson, Lingfeng Yan, William R Milner The observation of Pauli blocking of atomic spontaneous decay via direct measurements of the atomic population requires the use of longlived atomic gases where quantum statistics, atom recoil and cooperative radiative processes are all relevant. We develop a theoretical framework capable of simultaneously accounting for these effects and apply it to atoms featuring an effective $\Lambda$ level structure confined in a single 2D pancake or arrays of pancakes. We identify a parameter window in which a factor of two extension in the atomic lifetime clearly attributable to Pauli blocking should be experimentally observable in deeply degenerate gases with $\sim 10^{3} $ atoms. Consistent with these theory predictions, we experimentally observe a $\sim$20\% suppressed excited state decay rate in the moderately degenerate regime on the ${}^{1}\rm{S_0}{}^{3}\rm{P_1}$ transition in $^{87}$Sr atoms. 
Tuesday, May 31, 2022 2:42PM  2:54PM 
E05.00002: Excitation Spectrum and Superfluid Gap of an Ultracold Fermi Gas Hauke Biss, Lennart Sobirey, Niclas Luick, Markus Bohlen, Jami Kinnunen, Georg Bruun, Thomas Lompe, Henning Moritz Ultracold Fermi gases with tunable interactions have enabled the realization of the famous BECBCS crossover from a BoseEinstein condensate (BEC) of molecules to a BardeenCooperSchrieffer (BCS) superfluid of weakly bound Cooper pairs. Using Bragg spectroscopy, we measure the full momentumresolved lowenergy excitation spectrum of strongly interacting Fermi gases and directly observe the smooth transformation from a bosonic to a fermionic superfluid that takes place in the BECBCS crossover. Moreover, we determine the evolution of the superfluid gap from these spectra and find excellent agreement with previous experiments and selfconsistent Tmatrix calculations both in the BEC and crossover regime. However, towards the BCS regime, a calculation that includes the effects of particlehole correlations shows better agreement with our data. 
Tuesday, May 31, 2022 2:54PM  3:06PM 
E05.00003: Observing the effect of dimensionality on the stability of strongly interacting fermionic superfluids Niclas Luick, Lennart Sobirey, Hauke Biss, Markus Bohlen, Henning Moritz, Thomas Lompe We use ultracold Fermi gases as a model system to directly probe the influence of dimensionality on the stability of fermionic superfluids. Using momentumresolved Bragg spectroscopy, we measure the superfluid gap of of two and threedimensional homogeneous Fermi gases over a wide range of interaction strengths. We find that the superfluid gap follows a universal function of the chemical potential, irrespective of the dimensionality. Comparing our results with other fermionic superfluids suggests that strong correlations and short coherence lengths are more important for the stability of fermionic superfluids than the dimensionality of the system. 
Tuesday, May 31, 2022 3:06PM  3:18PM 
E05.00004: Realization of resonantly interacting Fermi mixtures of ^{6}Li and ^{53}Cr atoms Alessio Ciamei, Stefano Finelli, Massimo Inguscio, Andreas Trenkwalder, Andrea Simoni, Matteo Zaccanti We report on the realization of resonantly interacting Fermi mixtures of ^{6}Li and ^{53}Cr atoms. 
Tuesday, May 31, 2022 3:18PM  3:30PM 
E05.00005: Controlling persistent currents in fermionic rings via phase imprinting Giulia Del Pace, Klejdja Xhani, Alessandro Muzi Falconi, Marco Fedrizzi, Nicola Grani, Diego Hernandez Rajkov, Francesco Scazza, Woo Jin Kwon, Giacomo Roati Here I report on our recent results on exciting persistent currents in ringshaped atomic Fermi superfluids. By employing a phase imprinting technique, we populate finite and controllable circulation states throughout the BECBCS crossover. We make use of a second disk condensate as a local oscillator to extract the circulation state of the ring by means of an interferometric probe, which allows us to monitor the current in time. By increasing the number of phase imprinting pulses, we are able to deterministically populate high circulation states of the fermionic ring superfluids, which are observed to be as long lived as the atomic sample. Finally, we induce the current decay by inserting a defect inside the ring trap to trigger dissipation. In the BEC and BCS regime, the high circulation currents are observed to decay via the emission of vortices, in well agreement with GrossPitaevskii numerical simulation for the first case. On the other hand, in the UFG all the accessible circulation states are found to be robust against dissipation. Our work demonstrates phase imprinting as a powerful technique to control the circulation state of a superfluid, opening for further studies on superfluidity and dissipation of stronglyinteracting fermions. 
Tuesday, May 31, 2022 3:30PM  3:42PM 
E05.00006: Observation of Anomalous Decay in a Uniform ThreeComponent Fermi Gas Grant Schumacher, Gabriel Assumpcao, Derek Chen, Yunpeng Ji, Jere Makinen, Franklin Vivanco, Nir Navon We investigate the stability of a threecomponent Fermi gas with contact interactions. Starting with a quasihomogeneous ultracold gas in an optical box trap, we prepare a spin1like Fermi gas using the three lowest Zeeman levels of ^{6}Li and observe the resulting decay of the spin populations over time. We observe competition between threebody recombination of free atoms and twobodylike inelastic collision of atoms and dimers. We report the first observation of losses in a spinimbalanced, threecomponent mixture; the spinimbalanced system shows surprising dynamics that cannot be described by a simple loss rate expression. We propose an empirically determined loss rate expression which describes both balanced and imbalanced mixtures. 
Tuesday, May 31, 2022 3:42PM  3:54PM 
E05.00007: Optical Control of Interactions in an EnergySpace Spin Lattice Camen Royse, Ilya Arakelyan, John E Thomas A spin lattice in energyspace is created by a weaklyinteracting Fermi gas, which conserves the singleatom energy states over long time scales. Forward scattering produces effective longrange sitetosite couplings, which we control using optical fields. We demonstrate optical tuning of the sitetosite couplings by inducing spin waves over timescales of hundreds of milliseconds. This opticallycontrolled manybody system serves as a new platform for simulations of spin lattices and studies of information scrambling. 
Tuesday, May 31, 2022 3:54PM  4:06PM 
E05.00008: A Diagrammatic Monte Carlo study of the resonant Fermi Polaron Olga Goulko, Andrey Mishchenko, Nikolay V Prokofiev, Boris Svistunov The Fermi polaron is an impurity interacting with a sea of fermions. It is an exemplary system to study impurity problems, strongly imbalanced Fermi gases and quasiparticles. For strong interactions diagrammatic Monte Carlo provides a reliable tool to calculate various properties of the system quantitatively and from first principles. In my talk I will show how diagrammatic Monte Carlo, resummation techniques and numerical analytic continuation can be applied to obtain the spectral function of the resonant Fermi polaron, which can be measured in cold atoms experiments. 
Tuesday, May 31, 2022 4:06PM  4:18PM 
E05.00009: Probing molecular spectral functions in ultracold Fermi gases via Raman spectroscopy Oriana K Diessel, Richard Schmidt The detection of many strongly correlated phases remains a challenge in experimental physics. Here we present a theoretical proposal to directly detect the momentum resolved spectral function of molecular states in ultracold twocomponent Fermi mixtures, using conventional spectroscopic techniques in the quantum impurity limit. The detection of this quantity has remained so far elusive. We will then show how this new spectroscopic technique can be used to observe precursors of strongly correlated phases in Fermi mixtures, including possibly the FFLO phase, in excited states in the impurity limit. Our proposal will enable the detection of the dispersion relation and the excitation spectrum of composite particles dressed by a manybody environment. We further discuss possible experimental realizations. 
Tuesday, May 31, 2022 4:18PM  4:30PM 
E05.00010: Tunneling dynamics of small twocomponent Fermi systems Kevin MackFischer, Doerte Blume Tunneling is an inherently quantum mechanical process. Interactions between particles can speed the singleparticle tunneling dynamics up or slow it down; they can also trigger correlated tunneling of pairs or clusters. We will report on our theoretical work in progress on describing the tunneling dynamics of small twocomponent Fermi systems in an effectively onedimensional trap. We use the imaginary time evolution to prepare the initial state and real time evolution to simulate the system dynamics. The particle flux out of the trap is monitored and tunneling rates are extracted. We will discuss the numerical techniques such as the alternating direction implicit twodimensional CrankNicholson scheme, its efficiency, and initial results. Extensions to three dimensions (three onedimensional particles) will be discussed. 
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