Dynamical equilibration across a quenched phase transition in a trapped quantum gas

Abstract

The formation of an equilibrium quantum state from an uncorrelated thermal one through the dynamical crossing of a phase transition is a central question of non-equilibrium many-body physics. During such crossing, the system breaks its symmetry by establishing numerous uncorrelated regions separated by spontaneously-generated defects, whose emergence obeys a universal scaling law with the quench duration. Much less is known about the ensuing re-equilibrating or "coarse-graining" stage, which is governed by the evolution and interactions of such defects under system-specific and external constraints. In this work we perform a detailed numerical characterization of the entire non-equilibrium process, addressing subtle issues in condensate growth dynamics and demonstrating the quench-induced decoupling of number and coherence growth during the re-equilibration process. Our unique visualizations not only reproduce experimental measurements in the relevant regimes, but also provide valuable information in currently experimentally-inaccessible regimes.arXiv:1712.08074v1 [cond-mat.quant-gas]

Simulating cosmological supercooling with a cold-atom system

“…Stochastic Gross-Pitaevskii equations (SGPEs) are widely used for modeling atomic gases at and below the condensation temperature [17][18][19][20]26,27]. Here, we use the simple growth SPGPE [19,20], which has been successfully used to model experimental phase transitions [28,29]. Extension of the SPGPE to spinor and multicomponent condensates is described in Ref.…”

“…Values of γ from O(10 −4 ) to O(10 −2 ) have been used in previous work that made direct comparisons to experiment [28][29][30][31], making this a reasonable choice. We comment on the effect of γ later in the text.…”

Phase diagram of solitons in the polar phase of a spin-1 Bose-Einstein condensate

“…Generation of topological defects caused by spontaneous symmetry breaking (SSB) is a universal phenomenon constantly addressed in cosmology, high energy and condensed matter physics [1][2][3]. Depending on the type of SSB transition and the degrees of freedom of order parameters topological defects are created in various forms, such as vortices/strings [4,5], domain walls/solitons [6], hedgehogs/monopoles, or their composites. In the past decades, the multicomponent or spinful superfluids of liquid 3 He [7][8][9] and gaseous Bose-Einstein condensates (BECs) [10][11][12], which induce SSB in numerous ways because of their multiple degrees of freedom of order parameters, have served as a testing ground for the creation of novel topological defects.…”

Exploring the thermodynamics of spin-1 Bose gases with synthetic magnetization

“…Due to their rich phase diagram, spinor Bose gases have recently been promoted as an optimal system to study non-equilibrium dynamics. For example thermal quenches were used to cross over the BEC transition [30,31], and microwave dressing allowed to operate selectively on the Zeemen energy levels [32]. Our work opens new possibilities in performing isothermal quenches across different phases using the synthetic magnetization, a method that could be exploited in future experiments to study out-of-equilibrium physics in spinor systems.…”