Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session H6: Two-Dimensional Gases |
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Chair: Blair Blakie, University of Otago Room: 552AB |
Wednesday, May 25, 2016 10:30AM - 10:42AM |
H6.00001: Radiofrequency Spectroscopy and Thermodynamics of Fermi Gases in the 2D to Quasi-2D Dimensional Crossover Chingyun Cheng, Jayampathi Kangara, Ilya Arakelyan, John Thomas We tune the dimensionality of a strongly interacting degenerate $^{6}$Li Fermi gas from 2D to quasi-2D, by adjusting the radial confinement of pancake-shaped clouds to control the radial chemical potential. In the 2D regime with weak radial confinement, the measured pair binding energies are in agreement with 2D-BCS mean field theory, which predicts dimer pairing energies in the many-body regime. In the qausi-2D regime obtained with increased radial confinement, the measured pairing energy deviates significantly from 2D-BCS theory. In contrast to the pairing energy, the measured radii of the cloud profiles are not fit by 2D-BCS theory in either the 2D or quasi-2D regimes, but are fit in both regimes by a beyond mean field polaron-model of the free energy. [Preview Abstract] |
Wednesday, May 25, 2016 10:42AM - 10:54AM |
H6.00002: Observation of the Leggett-Rice effect in an ensemble of 2D Fermi gases Christopher Luciuk, Scott Smale, Stefan Trotzky, Haille Sharum, Tilman Enss, Joseph Thywissen Transport properties of unitary Fermi gases have been studied extensively in the past few years. Because of strong interparticle scattering at unitarity, many transport phenomenon, in particular the spin diffusivity, are observed to be bounded [1-4]. However, anomalously slow spin diffusion has been observed in two dimensions [2] and remains to be understood. Here we study the spin currents that arise as a result of a non-equilibrium magnetization in an ensemble of two dimensional Fermi gases. Spin currents possess both a dissipative and reactive component. The dissipative component – parameterized by the spin diffusivity – is a measure of the scattering rate. The reactive component describes a part of the spin current that precesses around the local magnetization known as the Leggett-Rice effect. Using a spin-echo sequence we measure both the amplitude and phase of magnetization dynamics to extract these two transport parameters at a range of interaction strengths near a Feshbach resonance. [1] A. Sommer, M. Ku, G. Roati, and M.W. Zwierlein, Nature 472, 201 (2011). [2] M. Koschorreck, D. Pertot, E. Vogt, and M. Kohl, Nat. Phys. 9, 405 (2013). [3] A.B. Bardon, et al., Science 344, 722 (2014). [4] S. Trotzky, et al., PRL 114, 015301 (2015). [Preview Abstract] |
Wednesday, May 25, 2016 10:54AM - 11:06AM |
H6.00003: Three-bosons in 2D with a magnetic field Seth Rittenhouse, Brad Johnson, Andrew Wray, Jose D'Incao Systems of interacting particles in reduced dimensions in the presence of external fields can exhibit a number of surprising behaviors, for instance the emergence of the fractional quantum Hall effect. Examining few-body interactions and effects can lead to significant insights within these systems. In this talk we examine a system of three bosons confined to two dimensions in the presence of a perpendicular magnetic field within the framework of the adiabatic hyperspherical method. For the case of zero-range, regularized pseudo-potential interactions, we find that the system is nearly separable in hyperspherical coordinates and that, away from a set of narrow avoided crossings, the full energy eigenspectrum as a function of the 2D s-wave scattering length is well described by ignoring coupling between adiabatic hyperradial potentials. In the case of weak attractive or repulsive interactions, we find the lowest three-body energy states exhibit even/odd parity oscillations as a function of total internal 2D angular momentum and that for weak repulsive interactions, the universal lowest energy interacting state has an internal angular momentum of M=3. We also discuss the effect of including finite range and higher partial-wave interactions. [Preview Abstract] |
Wednesday, May 25, 2016 11:06AM - 11:18AM |
H6.00004: Exciton-like molecules and interaction resonances in bilayer ultracold gases Marton Kanasz-Nagy, Eugene Demler, Gergely Zarand I will discuss how confinement effects in bilayer quantum gases can lead to interlayer molecular states, that appear both at positive and negative energies and even at layer separations many times larger than the interspecies scattering length. Similar to excitons in bilayer quantum wells, the lifetime of the molecules grows significantly with increasing layer separation, allowing for their detection in simple shaking experiments. Moreover, these molecular states also give rise to sharp interspecies Feshbach resonances, enabling one to control the interaction between the two species geometrically, simply by changing the layer separation. Rather counterintuitively, the species can be made strongly interacting, by separating them from each other. [M. Kanász-Nagy, E. A. Demler, and G. Zaránd, Phys. Rev. A 91, 032704 (2015)] [Preview Abstract] |
Wednesday, May 25, 2016 11:18AM - 11:30AM |
H6.00005: Local properties of the two-dimensional Hubbard model Jan Drewes, Luke Miller, Eugenio Cocchi, Chun Fai Chan, Daniel Pertot, Ferdinand Brennecke, Michael K\"{o}hl Quantum gases of interacting fermionic atoms in optical lattices promise to shed new light on the low-temperature phases of the Hubbard model such as spin-ordered phases, or in particular, on possible d-wave superconductivity. In this context it remains challenging to further reduce the temperature of the trapped gas. We experimentally realize the two-dimensional Hubbard model by loading a quantum degenerate Fermi gas of 40K atoms into a three-dimensional optical lattice geometry. By tuning the interaction between the two lowest hyperfine states to strong repulsion the two-dimensional Mott-insulator is created. High resolution absorption imaging in combination with radio-frequency spectroscopy is applied to spatially resolve the atomic distribution in a single layer in the vertical direction. This measurement scheme gives direct access to the local properties of the trapped gas and we present most recent data on the distribution of entropy and density-density fluctuations. [Preview Abstract] |
Wednesday, May 25, 2016 11:30AM - 11:42AM |
H6.00006: Critical Dynamics in Quenched 2D Atomic Gases F. Larcher, F. Dalfovo, N. P. Proukakis Non-equilibrium dynamics across phase transitions is a subject of intense investigations in diverse physical systems. One of the key issues concerns the validity of the Kibble-Zurek (KZ) scaling law for spontaneous defect creation. The KZ mechanism has been recently studied in cold atoms experiments [1,2]. Interesting open questions arise in the case of 2D systems, due to the distinct nature of the Berezinskii-Kosterlitz-Thouless (BKT) transition [3]. Our studies rely on the stochastic Gross-Pitaevskii equation. We perform systematic numerical simulations of the spontaneous emergence and subsequent dynamics of vortices in a uniform 2D Bose gas, which is quenched across the BKT phase transition in a controlled manner, focusing on dynamical scaling and KZ-type effects. By varying the transverse confinement, we also look at the extent to which such features can be seen in current experiments [4]. REFS: [1] Weiler et al., Nature 455, 948 (2008); Corman et al, Phys.Rev.Lett. 113, 135302 (2014); Navon et al., Science 347, 6218 (2015) [2] Lamporesi et al., Nat.Phys. 9, 656 (2013); Serafini et al., Phys.Rev.Lett. 115, 170402 (2015) [3] Jeli\'{c} et al., J.Stat. Mech. P02032 (2011) [4] Chomaz et al., Nat.Comm. 6, 6162 (2014). [Preview Abstract] |
Wednesday, May 25, 2016 11:42AM - 11:54AM |
H6.00007: Dynamics of Two Dimensional Bose Gases and the Role of Scale Invariance Jeff Maki The controllable study of dynamics has become commonplace in cold atom experiments. However, the theoretical exploration of dynamics has relied heavily on numerical simulations due to the vast complexity of dynamical many body problems. The situation is simplified in two dimensional Bose gases thanks to the presence of scale invariance. This symmetry is presumed to have an important effect on the dynamics of the system but has yet to be studied in the context of cold gases. In this talk we report a study of interacting two dimensional Bose gases and the role scale invariance plays on the system's dynamics. [Preview Abstract] |
Wednesday, May 25, 2016 11:54AM - 12:06PM |
H6.00008: Local Probing of Phase Coherence in a Strongly Interacting 2D Quantum Gas Niclas Luick, Jonas Siegl, Klaus Hueck, Kai Morgener, Thomas Lompe, Wolf Weimer, Henning Moritz The dimensionality of a quantum system has a profound impact on its coherence and superfluid properties. In 3D superfluids, bosonic atoms or Cooper pairs condense into a macroscopic wave function exhibiting long-range phase coherence. Meanwhile, 2D superfluids show a strikingly different behavior: True long-range coherence is precluded by thermal fluctuations, nevertheless Berezinskii-Kosterlitz-Thouless (BKT) theory predicts that 2D systems can still become superfluid. The superfluid state is characterized by an algebraic decay of phase correlations $g_1(r)\propto r^{-\tau/4}$, where the decay exponent $\tau$ is directly related to the superfluid density $n_s$ according to $\tau=4/(n_s \lambda_{\rm dB}^2)$. I will present local coherence measurements in a strongly interacting 2D gas of diatomic $^{6}$Li molecules. A self-interference technique allows us to locally extract the algebraic decay exponent and to reconstruct the superfluid density. We determine the scaling of the decay exponent with phase space density to provide a benchmark for studies of 2D superfluids in the strongly interacting regime. [Preview Abstract] |
Wednesday, May 25, 2016 12:06PM - 12:18PM |
H6.00009: Pair condensation in a spin-imbalanced 2D Fermi gas Debayan Mitra, Peter Brown, Peter Schauss, Stanimir Kondov, Waseem Bakr We study the phase diagram of the strongly-interacting spin-imbalanced Fermi gas in two dimensions, where the low dimensionality enhances correlations and phase fluctuations. Our interest is motivated by the connection of this system with superconductivity in the presence of a large Zeeman field. We observe pair condensation for a range of spin imbalance and interaction strengths. The measurement of the phase diagram opens the door for a detailed investigation of exotic phases such as the Sarma/broken pair phase and the elusive FFLO phase. [Preview Abstract] |
Wednesday, May 25, 2016 12:18PM - 12:30PM |
H6.00010: Controlling interactions in ultracold fermionic ytterbium-173 Moritz H\"ofer, Luis Riegger, Chrisitian Hofrichter, Diogo Rio Fernandes, Immanuel Bloch, Simon F\"olling The possibility to tune the interactions of ultracold atomic gases with an external magnetic field has become a vital tool for many quantum gas experiments. For fermionic ytterbium-173 both the $^1$S$_0$ ground state and $^3$P$_0$ metastable state have vanishing angular momentum $J=0$ and therefore no magnetic Feshbach resonances are expected. Here we report on the discovery of a novel type of Feshbach resonance, which was predicted to exist due to orbital-mixing interactions. It occurs universally for all hyperfine-state combinations of ytterbium-173 and is located at experimentally accessible magnetic fields. The scattering properties are characterized by inter-orbital cross-thermalization measurements in the bulk as well as high resolution clock-line spectroscopy in a three-dimensional lattice. Furthermore, we study the dynamics of a strongly interacting two-orbital quantum gas in two dimensions. [Preview Abstract] |
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