Stability of a Unitary Bose Gas

Fletcher, R.; Gaunt, Alexander L.; Navon, Nir; Smith, Robert P.; Hadzibabic, Zoran

doi:10.1103/physrevlett.111.125303

Cited by 95 publications

(122 citation statements)

References 40 publications

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“…These questions are closely related to the very existence of the unitary Bose gas on time scales larger than its thermalization time. Very recent experimental works indicate that the ultra-cold unitary Bose gas can indeed be stabilized on appreciable time scales 11,14,15 .…”

Section: Discussionmentioning

confidence: 99%

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Efimov-driven phase transitions of the unitary Bose gas

Piatecki

Krauth

2014

Nat Commun

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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. Here we use 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. We discuss the prospects of observing the proposed phase transitions in cold-atom systems.

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Section: Discussionmentioning

confidence: 99%

“…However, the macroscopic many-body properties of the unitary Bose gas have remained unknown. The understanding of its thermodynamic behaviour is of great importance, especially as the experimental stability of the unitary Bose gas of cold atoms has been reported for appreciable time scales 11,14,15 .…”

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confidence: 99%

Efimov-driven phase transitions of the unitary Bose gas

Piatecki

Krauth

2014

Nat Commun

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“…In the extreme case of unitarity, where a → ∞, the interatomic distance, n −1/3 , remains the only physically relevant length scale, and the unitary Bose gas [29][30][31][32][33][34][35][36][37] is expected to display universal properties akin to those of a Fermi gas at unitarity [38][39][40]. The prospect of a well-defined unitary limit was brightened by experiments on dilute thermal Bose gases [41,42]. At unitarity, on purely dimensional grounds, both the three-body loss and the equilibration rates will be of the same order of magnitude as the Fermi energy [38], ǫ F = (ω F = k 2 F /2m), where k F = (6π 2 n) 1/3 is the Fermi momentum.…”

Section: Introductionmentioning

confidence: 99%

Nonequilibrium states of a quenched Bose gas

Kain

Ling

2014

Phys. Rev. A

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Yin and Radzihovsky [1] recently developed a self-consistent extension of a Bogoliubov theory, in which the condensate number density nc is treated as a mean field that changes with time, in order to analyze a JILA experiment by Makotyn et al.[2] on a 85 Rb Bose gas following a deep quench to a large scattering length. We apply this theory to construct a closed set of equations that highlight the role ofṅc, which is to induce an effective interaction between quasiparticles. We show analytically that such a system supports a steady state characterized by a constant condensate density and a steady but periodically changing momentum distribution, whose time average is described exactly by the generalized Gibbs ensemble. We discuss how theṅc-induced effective interaction, which cannot be ignored on the grounds of the adiabatic approximation for modes near the gapless Goldstone mode, can significantly affect condensate populations and Tan's contact for a Bose gas that has undergone a deep quench.

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“…For bosonic atoms, however, this route to strong interactions is stymied by the fact that three-body inelastic collisions increase as a to the fourth power [21][22][23]. This circumstance has limited experimental investigation of Bose gases with increasing interaction strength to studying either non-quantum-degenerate gases [24,25] or BECs with modest interaction strengths (na 3 < 0.008, where n is the atom number density) [9][10][11][12].The problem is that the loss rate scales as n 2 a 4 while the equilibration rate scales as na 2 v, where v is the average velocity. Thus, it would seem that the losses will always dominate as a is increased to ∞.…”

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confidence: 99%

Universal dynamics of a degenerate unitary Bose gas

et al. 2014

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From neutron stars to high-temperature superconductors, 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 due to limited experimental probes. While an ultracold atomic Bose gas with tunable interactions (characterized by its scattering length, a) had been proposed as an alternative strongly interacting Bose system [1][2][3][4][5][6][7][8] , experimental progress [9][10][11][12] 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, i.e. to a = ∞. 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.A powerful feature of atom gas experiments that provides access to these new regimes is the ability to change the interaction strength using a magnetic-field Feshbach resonance [13]. In particular, at the resonance location, a is infinite. For atomic Fermi gases [14][15][16][17][18][19][20], accessing this regime by adiabatically changing a led to the achievement of superfluids of paired fermions and enabled investigation of the crossover from superfluidity of weakly bound pairs, analogous to the Bardeen-Cooper-Schrieffer (BCS) theory of superconductors, to Bose-Einstein condensation (BEC) of tightly bound molecules [16,17]. For bosonic atoms, however, this route to strong interactions is stymied by the fact that three-body inelastic collisions increase as a to the fourth power [21][22][23]. This circumstance has limited experimental investigation of Bose gases with increasing interaction strength to studying either non-quantum-degenerate gases [24,25] or BECs with modest interaction strengths (na 3 < 0.008, where n is the atom number density) [9][10][11][12].The problem is that the loss rate scales as n 2 a 4 while the equilibration rate scales as na 2 v, where v is the average velocity. Thus, it would seem that the losses will always dominate as a is increased to ∞. Even if we were to forsake thermal equilibrium and suddenly change a in order to project a weakly interacting BEC onto strong interactions [12,[26][27][28], one might expect that three-body losses would still dominate the ensuing dynamics for large a. In this work, however, we use this approach to take a BEC to the unitary gas regime, and we observe dynamics that in fact saturate on a timescale shorter than that set by three-body losses and that exhibit universal scaling with density.

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Stability of a Unitary Bose Gas

Cited by 95 publications

References 40 publications

Efimov-driven phase transitions of the unitary Bose gas

Efimov-driven phase transitions of the unitary Bose gas

Nonequilibrium states of a quenched Bose gas

Universal dynamics of a degenerate unitary Bose gas

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