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 G09: Fermi Gases and Bose-Fermi MixturesLive
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Chair: Cheng Chin, University of Chicago Room: Portland 256 |
Wednesday, June 3, 2020 8:00AM - 8:12AM Live |
G09.00001: Collective Excitations in Bose-Fermi Mixture Carsten Robens, Yiqi Ni, Zoe Yan, Alexander Chuang, Martin Zwierlein Low-lying collective excitations are sensitive probes to quantum many-body systems. In particular, quasiparticle properties and the quantum gas’s equation of state are studied through these elementary excitations. We focus on exploring the Bose-Fermi mixture in the fermionic impurity limit, which exhibits rich many-body phase diagram and dynamics. The mixture is created by immersing fermionic $^{40}$K atoms into a $^{23}$Na Bose-Einstein condensate (BEC). We optically excite dipole and other low-lying collective modes and study the Bose-Fermi mixture response upon varying interspecies interaction strength and temperature. Our experiments reveal a collisionless to hydrodynamic transition of fermionic impurities. [Preview Abstract] |
Wednesday, June 3, 2020 8:12AM - 8:24AM Live |
G09.00002: Spontaneous formation of polar superfluid droplets in a p-wave interacting Bose gas Zehan Li, Jian-song Pan, W. Vincent Liu We study the quantum fluctuations in the condensates of a mixture of bosonic atoms and molecules with interspecies p-wave interaction. Our analysis shows that the quantum phase of coexisting atomic and molecular condensates is unstable at the mean-field level. Unlike the mixture of s-wave interaction, the Lee-Huang-Yang correction of p-wave interaction is unexpectedly found here to exhibit an opposite sign with respect to its mean-field term above a critical particle density. This quantum correction to the mean-field energy provides a remarkable mechanism to self-stabilize the phase. The order parameter of this superfluid phase carries opposite finite momenta for the two atomic species while the molecular component is a polar condensate. Such a correlated order spontaneously breaks a rich set of global U(1) gauge, atomic spin, spatial rotation and translation, and time-reversal symmetries. For potential experimental observation, the phenomenon of anisotropic polar superfluid droplets is predicted to occur when the particle number is kept finite. [Preview Abstract] |
Wednesday, June 3, 2020 8:24AM - 8:36AM Live |
G09.00003: Quantum degenerate mixtures of Cs and Yb. Kali Wilson, Alexander Guttridge, Jack Segal, Simon Cornish We have created quantum degenerate Bose-Bose mixtures of Cs + $^{174}$Yb and Cs + $^{170}$Yb in a bichromatic optical dipole trap. By tuning the interaction strength of Cs using a low-field Feshbach resonance we explore the stability of the Cs + $^{174}$Yb degenerate mixture and observe collapse of the Cs condensate due to the interaction with $^{174}$Yb. These results build upon recent interspecies thermalization and two-photon photoassociation measurements, which allowed more accurate calculation of the interspecies scattering lengths for all seven Yb isotopes, and identification of experimentally-feasible Feshbach resonances for magnetoassociation of CsYb molecules. We will report on recent progress from the Durham CsYb experiment including the demonstration of dual-degenerate Bose-Bose mixtures, observation of a Cs + $^{173}$Yb interspecies Feshbach resonance, and the implementation of Cs-blind optical potentials. We will discuss prospects for exploiting the unique advantages of Cs-Yb mixtures for studies of beyond-mean-field physics, including mass-imbalanced quantum liquid droplets where quantum fluctuations stabilize against mean-field collapse. [Preview Abstract] |
Wednesday, June 3, 2020 8:36AM - 8:48AM On Demand |
G09.00004: Normal state spin susceptibility in the BEC-BCS crossover region. Yun Long, Feng Xiong, Colin Parker The magnetic properties of Fermi gases around the BEC-BCS crossover is a topic of interest for its connection to strongly interacting material systems like the high-Tc cuprates. In particular, the spin susceptibility of the Fermi gas is a quantity that can be directly compared across these two very different physical platforms, and one in which the phenomenon of ``pseudogap'' has an established signature, at least on the material side. To this end, we develop a method which use a radiofrequency (RF) dressed spin state to measure the spin susceptibility of a trapped lithium-6 spin mixture near the BEC-BCS crossover region at temperatures from well above the Fermi temperature down to the critical point of the superfluid phase transition. In this talk, I will present our recent results and a comparison to theoretical calculations. [Preview Abstract] |
Wednesday, June 3, 2020 8:48AM - 9:00AM On Demand |
G09.00005: Breaking Scale Invariance: The role of the effective range on the bulk viscosity in s- and p-wave gases Jeff Maki, Shizhong Zhang We investigate the role of the effective range on the bulk viscosity of s- and p-wave gases. Even At resonance, the presence of the effective range breaks the scale invariance of the system, and hence results in a non-zero bulk viscosity. However, we show that the effective range has fundamental differences in the two cases. In the s-wave case, the role of the effective range is perturbative, and its contribution to the bulk viscosity vanishes when the effective range tends to zero. On the other hand, the effective range in p-wave gases will lead to a non-zero bulk viscosity, even in the zero-range limit. We illustrate this difference by computing the bulk viscosity spectral function in the high temperature limit, and by comparing the high-frequency tails, and sum rules, for both s- and p-wave gases. [Preview Abstract] |
Wednesday, June 3, 2020 9:00AM - 9:12AM On Demand |
G09.00006: Breathing mode of a BEC immersed in a Fermi sea Piotr Grochowski, Tomasz Karpiuk, Miros\l{}aw Brewczyk, Kazimierz Rz\c{a}\.zewski By analyzing breathing mode of a Bose-Einstein condensate repulsively interacting with a polarized fermionic cloud, we further the understanding of a Bose-Fermi mixture recently realized by Lous et al. [\textit{Phys. Rev. Lett.} \textbf{120}, 243403]. We show that a hydrodynamic description of a domain wall between bosonic and fermionic atoms reproduces experimental data of Huang et al. [\textit{Phys. Rev. A} \textbf{99}, 041602(R)]. Two different types of interaction renormalization are explored, based on lowest order constrained variational and perturbation techniques. In order to replicate nonmonotonic behavior of the oscillation frequency observed in the experiment, temperature effects have to be included. We find that the frequency down-shift is caused by the fermion-induced compression and rethermalization of the bosonic species as the system is quenched into the strongly interacting regime. [Preview Abstract] |
Wednesday, June 3, 2020 9:12AM - 9:24AM On Demand |
G09.00007: Transport of Spin and Mass at Normal-Superfluid Interfaces in the Unitary Fermi Gas Ding Zhang, Ariel Sommer Strongly interacting Fermi gases provide a platform for studying non-equilibrium and transport properties of strongly correlated fermions. We consider the interface between a strongly polarized normal gas and a weakly polarized superfluid out of equilibrium, and examine the mass and spin current across the interface. To calculate the transport currents, we implement a mean-field framework in which the Hartree energy and superfluid gap are obtained from experimentally determined equations of state and excitation spectra. For any initial conditions of the densities, polarizations, and temperatures in both regions, our model provides a prediction of the instantaneous net and spin current across the interface. In our results, we show, for representative initial conditions, how spin current can be understood in terms of the threshold for creating excitations in the superfluid and the importance of Andreev reflection to the net (mass) current. Our work provides a comparison for future experimental measurements of transport at normal-superfluid interfaces. Finally, we provide an outlook on the calculation of shot noise on the transport current. [Preview Abstract] |
Wednesday, June 3, 2020 9:24AM - 9:36AM Not Participating |
G09.00008: Interactions and Dynamics of Bosons Embedded in a Fermi Gas Krutik Patel, Geyue Cai, B.J. DeSalvo, Cheng Chin Bosons immersed in a degenerate Fermi gas are predicted to interact at long range through excitations of the Fermi surface via the RKKY (Ruderman-Kittel-Kasuya-Yosida) mechanism. This interaction is expected to exhibit oscillations from attractive to repulsive akin to Friedel oscillation with a length scale set by the Fermi energy. We study fermion-mediated interactions based on quantum degenerate mixtures of bosonic $^{133}$Cs and fermionic $^6$Li, where the large mass-imbalance leads to a small Bose condensate immersed in a much larger degenerate Fermi gas. We employ high-resolution microscopy and a digital micro-mirror device to facilitate detection and control of the mixture at the one micron length scale. We will discuss schemes and progress towards direct observation of the long-ranged interactions mediated by the Fermi gas. [Preview Abstract] |
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