Bulletin of the American Physical Society
45th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 59, Number 8
Monday–Friday, June 2–6, 2014; Madison, Wisconsin
Session P2: Invited Session: Strongly Interacting Bose Gases |
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Chair: Peter Engels, Washington State University Room: Ballroom CD |
Thursday, June 5, 2014 4:00PM - 4:30PM |
P2.00001: Universal dynamics of a degenerate unitary Bose gas Invited Speaker: Deborah Jin Strongly interacting many-body systems at or near quantum degeneracy are a rich source of intriguing phenomena. The microscopic structure of the first-discovered quantum fluid, superfluid liquid helium, is difficult to access owing to limited experimental probes. Although an ultracold atomic Bose gas with tunable interactions (characterized by its scattering length, $a)$ had been proposed as an alternative strongly interacting Bose system, experimental progress has been limited by its short lifetime. Here we present time-resolved measurements of the momentum distribution of a Bose-condensed gas that is suddenly jumped to unitarity, where a$=\infty $. Contrary to expectation, we observe that the gas lives long enough to permit the momentum to evolve to a quasi-steady-state distribution, consistent with universality, while remaining degenerate. Investigations of the time evolution of this unitary Bose gas may lead to a deeper understanding of quantum many-body physics. [Preview Abstract] |
Thursday, June 5, 2014 4:30PM - 5:00PM |
P2.00002: Efimov-driven phase transitions of the unitary Bose gas Invited Speaker: Werner Krauth Initially predicted in nuclear physics, Efimov trimers are bound configurations of three quantum particles that fall apart when any one of them is removed. They open a window into a rich quantum world that has become the focus of intense experimental and theoretical research, as the region of unitary interactions, where Efimov trimers form, is now accessible in cold-atom experiments. We have used a path-integral Monte Carlo algorithm backed up by theoretical arguments to show that unitary bosons undergo a first-order phase transition from a normal gas to a superfluid Efimov liquid, bound by the same effects as Efimov trimers. A triple point separates these two phases and another superfluid phase, the conventional Bose-Einstein condensate, whose coexistence line with the Efimov liquid ends in a critical point. At the end of the talk, I discuss the prospects of observing the proposed phase transitions in cold-atom systems. [Preview Abstract] |
Thursday, June 5, 2014 5:00PM - 5:30PM |
P2.00003: From unitary to uniform Bose gases Invited Speaker: Zoran Hadzibabic In this talk I will give an overview of our recent experiments on Bose gases in extreme interaction regimes. In one limit, we studied the stability of a unitary Bose gas, with strongest possible interactions allowed by quantum mechanics [1]. In the other limit, we studied purely quantum-statistical ideal-gas phenomena, such as the quantum Joule-Thomson effect [2], by achieving Bose-Einstein condensation in a quasi-uniform potential of an optical-box trap [3]. \\[4pt] [1] Stability of a Unitary Bose Gas, R. J. Fletcher, A. L. Gaunt, N. Navon, R. P. Smith and Z. Hadzibabic, Phys. Rev. Lett. 111, 125303 (2013).\\[0pt] [2] Quantum Joule-Thomson Effect in a Saturated Homogeneous Bose Gas, T. F. Schmidutz, I. Gotlibovych, A. L. Gaunt, R. P. Smith, N. Navon, and Z. Hadzibabic, Phys. Rev. Lett. 112, 040403 (2014).\\[0pt] [3] Bose-Einstein Condensation of Atoms in a Uniform Potential, A. L. Gaunt, T. F. Schmidutz, I. Gotlibovych, R. P. Smith, and Z. Hadzibabic, Phys. Rev. Lett. 110, 200406 (2013). [Preview Abstract] |
Thursday, June 5, 2014 5:30PM - 6:00PM |
P2.00004: Universality and scaling in the $N$-body sector of Efimov physics Invited Speaker: Mario Gattobigio In this talk I will illustrate the universal behavior that we have found inside the window of Efimov physics for systems made of $N\le 6$ particles~[1]. We have solved the Schr\"odinger equation of the few-body systems using different potentials, and we have changed the potential parameters in such a way to explore a range of two-body scattering length, $a$, around the unitary limit, $|a| \rightarrow \infty$. The ground- ($E_N^0$) and excited-state ($E^1_N)$ energies have been analyzed by means of a recent-developed method which allows to remove finite-range effects~[2]. In this way we show that the calculated ground- and excited-state energies collapse over the same universal curve obtained in the zero-range three-body systems. Universality and scaling are reminiscent of critical phenomena; in that framework, the critical point is mapped onto a fixed point of the Renormalization Group (RG) where the system displays scale-invariant (SI) symmetry. A consequence of SI symmetry is the scaling of the observables: for different materials, in the same class of universality, a selected observable can be represented as a function of the control parameter and, provided that both the observable and the control parameter are scaled by some material-dependent factor, all representations collapse onto a single universal curve. Efimov physics is a more recent example of universality, but in this case the physics is governed by a limit cycle on the RG flow with the emergence of a discrete scale invariance (DSI). The scaling of the few-body energies can be interpreted as follow: few-body systems (at least up to $N=6$), inside the Efimov window, belong to the same class of universality, which is governed by the limit cycle. These results can be summarized by the following formula \begin{equation} E_N^n/E_2 = \tan^2\xi \\ \qquad \kappa^n_N a_B + \Gamma^n_N = \frac{\mathrm{e}^{-\Delta(\xi)/2s_0}}{\cos\xi}\,. \end{equation} where the function $\Delta(\xi)$ is universal and it is determined by the three-body physics, and $s_0=1.00624$. The parameter $\kappa^n_N$ appears as a scale parameter and the shift $\Gamma_n^N$ is a finite-range scale parameter introduced to take into account finite-range corrections~[2].\\[4pt] [1] M. Gattobigio and A. Kievsk, arXiv:1309.1927 (2013).\\[0pt] [2] A. Kievsky and M. Gattobigio, Phys. Rev. A {\bf 87}, 052719 (2013). [Preview Abstract] |
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