Bulletin of the American Physical Society
2013 Joint Meeting of the APS Division of Atomic, Molecular & Optical Physics and the CAP Division of Atomic, Molecular & Optical Physics, Canada
Volume 58, Number 6
Monday–Friday, June 3–7, 2013; Quebec City, Canada
Session G3: Strongly Interacting BECs |
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Chair: Fei Zhou, University of British Columbia Room: 202 |
Wednesday, June 5, 2013 8:00AM - 8:12AM |
G3.00001: Interacting Bose Gases Near Four Spatial Dimensions Shaojian Jiang, Wuming Liu, Gordon Semenoff, Fei Zhou Recently, interacting Bose gases at large positive scattering lengths can be experimentally investigated on the upper branch of a Feshbach resonance, which motivated more theoretical work. We proposed a new perspective to this problem by turning to $4$ spatial dimensions, and established a controllable expansion near $4$ spatial dimensions based on a $4-\epsilon$ analysis. Solving for the chemical potential shows the existence of a critical scattering length, at which the chemical potential reaches a maximum value and the many-body instability sets in. This is consistent with the result obtained by one of the authors (F.Z.) and his collaborators in $3$ dimensions. [Preview Abstract] |
Wednesday, June 5, 2013 8:12AM - 8:24AM |
G3.00002: Equations of State of Strongly Interacting Two-dimensional Bose Gases Li-Chung Ha, Chen-Lung Hung, Xibo Zhang, Ulrich Eismann, Shih-Kuang Tung, Eric L. Hazlett, Cheng Chin We study strongly interacting two-dimensional Bose gases based on \textit{in situ} density profiles of the sample in the superfluid and critical fluctuation regimes. By using a Feshbach resonance and imposing an optical lattice we are able to achieve strong interactions. In the superfluid phase, the measured compressibility deviates from the mean-field prediction when the interaction is strong, and are in better agreement with the renormalization calculation. Near the critical point of the superfluid transition, we find that the equations of state scale universally with respect to the interaction strength for the strengths we investigate. This allows for the extraction of critical chemical potentials and densities as well as the renormalized interactions strengths. We compare these results to the mean-field, classical field, Monte Carlo, and renormalization calculations. [Preview Abstract] |
Wednesday, June 5, 2013 8:24AM - 8:36AM |
G3.00003: Strongly interacting Bose gases F. Chevy, B.S. Rem, A.T. Grier, I. Ferrier-Barbut, U. Eismann, F. Werner, N. Navon, C. Salomon, D.S. Petrov, T. Langen, L. Khaykovich Contrary to Fermi systems, the quantitative experimental study of Bose gases have been limited to the weakly interacting regime, due to a strong increase of three-body recombination near Feshbach resonances. In this talk, we will present a quantitative study of the three-body recombination rate at unitarity and show that a unitary Bose gas can be stabilized at high temperature [1]. We will demonstrate that, contrary to Arrhenius's law, the rate of molecule formation follows a $1/T^2$ law dictated by the coupling to the attractive universal Efimow channel. Finally, we will discuss the influence of losses on the thermodynamical properties of the system. \\[4pt] [1] B. Rem {\em et al.} arXiv:1212.5274. [Preview Abstract] |
Wednesday, June 5, 2013 8:36AM - 8:48AM |
G3.00004: What happens to a BEC at unitarity? Philip Makotyn, Catherine Klauss, Eric Cornell, Deborah Jin Understanding many-body quantum systems with interactions, especially strong interactions, represents an important challenge in physics. While Bose-Einstein condensates (BEC) in ultracold atomic gases provide an accessible system with controllable interactions, historically, strongly interacting BECs have been difficult to study because these systems are inherently unstable due to three-body inelastic collisions. We report on work probing strongly interacting $^{85}Rb$ BEC at unitarity using a Feshbach resonance to quickly change the interaction strength. We observe dynamics of the gas before the cloud has lost many atoms or significantly changed its density. [Preview Abstract] |
Wednesday, June 5, 2013 8:48AM - 9:00AM |
G3.00005: Impurity bubbles in a BEC Eddy Timmermans, Alina Blinova, Malcolm Boshier Polarons (particles that interact with the self-consistent deformation of the host medium that contains them) self-localize when strongly coupled. Dilute Bose-Einstein condensates (BECs) doped with neutral distinguishable atoms (impurities) and armed with a Feshbach-tuned impurity-boson interaction provide a unique laboratory to study self-localized polarons. In nature, self-localized polarons come in two flavors that exhibit qualitatively different behavior: In lattice systems, the deformation is slight and the particle is accompanied by a cloud of collective excitations as in the case of the Landau-Pekar polarons of electrons in a dielectric lattice. In natural fluids and gases, the strongly coupled particle radically alters the medium, e.g. by expelling the host medium as in the case of the electron bubbles in superfluid helium. We show that BEC-impurities can self-localize in a bubble, as well as in a Landau-Pekar polaron state. The BEC-impurity system is fully characterized by only two dimensionless coupling constants. In the corresponding phase diagram the bubble and Landau-Pekar polaron limits correspond to large islands separated by a cross-over region. The same BEC-impurity species can be adiabatically Feshbach steered from the Landau-Pekar to the bubble regime. [Preview Abstract] |
Wednesday, June 5, 2013 9:00AM - 9:12AM |
G3.00006: Observation of critical behavior at the dissipative Dicke phase transition Renate Landig, Rafael Mottl, Ferdinand Brennecke, Kristian Baumann, Tobias Donner, Tilman Esslinger We experimentally study critical behavior at the Dicke quantum phase transition, realized by coupling the external degree of freedom of a Bose-Einstein condensate to the light field in a high-finesse optical cavity. We use the natural dissipation channel of the cavity to observe density fluctuations of the gas in real time. The corresponding measurement backaction introduces additional fluctuations in the atomic gas and changes the critical behavior of the system. A correlation analysis of the light exiting the cavity reveals the diverging time scale of the fluctuation dynamics, in agreement with the experimentally observed mode softening in the excitation spectrum. This analysis also allows us to extract a damping rate for the external degree of freedom of the atoms. We quantitatively compare our measurements with a theoretical model taking into account both cavity and atomic dissipation channels. Our experiment allows for a high degree of control of all parameters and constitutes a model system for the investigation of non-equilibrium phase transitions. Future directions of the experiment include Bose-Hubbard physics with cavity-mediated long-range interactions and self-organization in lower dimensions. [Preview Abstract] |
Wednesday, June 5, 2013 9:12AM - 9:24AM |
G3.00007: Stability analysis of two-dimensional Bose-Einstein condensates in the presence of a Gaussian potential Masaya Kunimi, Yusuke Kato Breakdown of superfluidity due to the nucleation of vortices has been investigated by many researchers [1,2]. However, the underlying mechanism of the instability of the nucleation of vortices is not clear. We investigate the stability of superflow states in two-dimensional Bose-Einstein condensates in the presence of a Gaussian potential by solving the Gross-Pitaevskii (GP) equation and the Bogoliubov equation. Although the system does not exhibit the Landau instability and dynamical instability, we find that the excitation energy of the first excited state in a finite system decreases rapidly toward zero near the critical velocity and the dynamical density fluctuations due to the low-lying normal mode increase. These results suggest that the breakdown of superfluidity can be regarded as dynamical critical phenomena. We discuss the relation between the breakdown of the superfluidity and the bifurcation structure of the stationary solution of the GP equation [3].\\[4pt] [1] T. Frisch, Y. Pomeau, and S. Rica, Phys. Rev. Lett. 69, 1644 (1992), C. Huepe and M-E. Brachet, Physica D, 140, 126 (2000).\\[0pt] [2] C. Raman et al., Phys. Rev. Lett. 83, 2502 (1999), S. Inouye et al., Phys. Rev. Lett. 87, 080402 (2001).\\[0pt] [3] Y. Kato and S. Watabe, Phys. Rev. Lett. 105, 035302 (2010). [Preview Abstract] |
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