Bulletin of the American Physical Society
48th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 62, Number 8
Monday–Friday, June 5–9, 2017; Sacramento, California
Session J2: Strongly interacting quantum gasesInvited
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Chair: Martin Zwierlein, Massachusetts Institute of Technology Room: 306-307 |
Wednesday, June 7, 2017 2:00PM - 2:30PM |
J2.00001: Impurities strongly interacting with a Fermi sea Invited Speaker: Rudolf Grimm Impurities immersed in a Fermi sea show a wealth of exciting phenomena when the interaction is tuned via a Feshbach resonance. We report on experiments with fermionic or bosonic potassium atoms in a large, deeply degenerate Fermi sea of $^6$Li. In the case of fermionic impurities ($^{41}$K), we focus on the low-concentration limit and apply a Ramsey technique to study the fast response of the impurities to sudden changes of the interaction strength [Cetina et al., Science 354, 96 (2016)]. For near-resonant conditons, we observe the formation dynamics of quasiparticles (Fermi polarons) in real time and, in the resonance case, an interference between the repulsive and the attractive quasiparticle branch. For bosons ($^{41}$K) in the Fermi sea, a small condensate is formed, which then acts as a mesoscopic impurity. For strongly repulsive conditions we find phase separation, such that the condensate is in the center of the Fermi sea and compressed by the fermion pressure. We show that three-body recombination can be used to probe the spatial overlap at the interface between the two species. The comparison with a theoretical model reveals behavior beyond the local-density approximation. We also study collective modes of the BEC in the Fermi gas across the transition to the phase-separated state, demonstrating dramatic changes of the collective mode frequencies. [Preview Abstract] |
Wednesday, June 7, 2017 2:30PM - 3:00PM |
J2.00002: Strongly interacting bulk Bose gases Invited Speaker: Zoran Hadzibabic I will give an overview of our recent experiments on strongly interacting Bose gases, produced in either a harmonic trap or the uniform potential of an optical box trap. Our recent work includes the interferometric measurement of the three-body contact in the unitary Bose gas, the measurement of the quantum depletion in a homogeneous strongly-interacting BEC, and studies of the universal decay dynamics in the homogeneous degenerate unitary Bose gas. [Preview Abstract] |
Wednesday, June 7, 2017 3:00PM - 3:30PM |
J2.00003: Bloch oscillations in the absence of a lattice Invited Speaker: Hanns-Christoph Naegerl We experimentally study the dynamics of strongly-correlated quantum many-body systems of ultracold atoms with particular focus on bosons confined to one-dimensional geometry. We have investigated the quantum motion of an impurity atom that is immersed in a strongly interacting Bose liquid and is subject to an external force [1]. We find that the momentum distribution of the impurity exhibits characteristic Bragg reflections at the edge of an emergent Brillouin zone. While Bragg reflections are typically associated with lattice structures, in our strongly correlated quantum liquid they result from the interplay of short-range crystalline order and kinematic constraints on the many-body scattering processes in the one-dimensional system. As a consequence, the impurity exhibits periodic dynamics that we interpret as Bloch oscillations. These arise even though the quantum liquid is translationally invariant. Our observations are supported by large-scale numerical simulations. [1] F. Meinert et al., arXiv:1608.08200 (2016). [Preview Abstract] |
Wednesday, June 7, 2017 3:30PM - 4:00PM |
J2.00004: Bragg spectroscopy of near-homogeneous Fermi gases Invited Speaker: Christopher Vale We have used Bragg spectroscopy to probe the excitation spectra of strongly interacting Fermi gases in the low and high momentum regimes. Using two laser beams focused into the center of trapped clouds we obtain Bragg spectra of systems with near-uniform density. At low momentum, below the superfluid transition temperature, the Bogoliubov-Anderson phonon mode is the dominant feature of the excitation spectra and single-particle excitations become visible for energies larger than twice the pairing gap. The respective frequencies of the phonon mode and the onset of single-particle excitations provide direct measures of the speed of sound and pairing gap. At high momentum, focused beam Bragg spectroscopy allows the determination of Tan’s universal contact parameter in a homogeneous system. We make use of sum-rules to map the temperature dependence of the contact and internal energy of Fermi gases at unitarity from our Bragg spectra. [Preview Abstract] |
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