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SUMMARY:Relaxation to Equilibrium and Emergence of Long-range Order in a T
 wo-Dimensional Quantum Vortex Gas - Hayder Salman (University of East Angl
 ia)
DTSTART:20221206T113000Z
DTEND:20221206T120000Z
UID:TALK183773@talks.cam.ac.uk
DESCRIPTION:We study the relaxation of a two-dimensional (2D) ultracold Bo
 se gas from a nonequilibrium initial state containing vortex excitations i
 n experimentally realizable traps.  We show that the subsystem of vortex g
 as excitations results in the spontaneous emergence of a coherent superflu
 id flow with a nonzero coarse-grained vorticity field. The stream function
  of this emergent quasiclassical 2D flow is governed by a Poisson-Boltzman
 n equation.  Numerical simulations of a neutral point vortex model and a B
 ose gas governed by the 2D Gross-Pitaevskii equation in a square trap reve
 al that a large-scale flow field with net angular momentum emerges that is
  consistent with predictions of the Poisson-Boltzmann equation.  The theor
 y presented is subsequently verified in recent experimental work focusing 
 on the turbulent relaxation dynamics of a two-dimensional chiral vortex ga
 s. Using carefully designed experimental forcing protocols to inject vorti
 ces into the system\,  we are able torealize equilibria spanning the full 
 phase diagram of the vortex gas\, including vortex states near zero temper
 ature\,  infinite temperature\,  and negative absolute temperatures. The r
 esulting experimentally measured long-time vortex distributions are found 
 to be in excellent agreement with the mean-field predictions of the Poisso
 n Boltzmann equation. This allows us to verify that\, during the relaxatio
 n dynamics\, the vortex excitations evolve to a state that maximises the e
 ntropy of the vortex gas.
LOCATION:Seminar Room 1\, Newton Institute
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