The new physics of non-equilibrium condensates: insights from classical dynamics

Using the exact eigenstates of the inhomogeneous Dicke model obtained by numerically solving the Bethe equations, we study the decay of bosonic excitations due to the coupling of the mode to an ensemble of two-level (spin 1/2) systems. We compare the quantum time-evolution of the bosonic mode population with the mean-field description which, for a few bosons agree up to a relatively long Ehrenfest time. We demonstrate that additional excitations lead to a dramatic shortening of the period of validity of the mean-field analysis. However, even in the limit where the number of bosons equal the number of spins, the initial instability remains adequately described by the meanfield approach leading to a finite, albeit short, Ehrenfest time. Through finite size analysis, we also present indications that the mean-field approach could still provide an adequate description for thermodynamically large systems even at long times. However, for mesoscopic systems one cannot expect it to capture the behavior beyond the initial decay stage in the limit of an extremely large number of excitations.

Section: Mean-field Analysismentioning

confidence: 99%

Nonequilibrum dynamics in the strongly excited inhomogeneous Dicke model

Sträter¹,

Tsyplyatyev²,

Faribault³

2012

“…A population with the form of a Fermi distribution could therefore condense due to a dynamical version of the BCS instability. 9,13 The remainder of this paper is structured as follows. In Sec.…”

Section: Introductionmentioning

confidence: 99%

Quantum condensation from a tailored exciton population in a microcavity

Eastham

Phillips

2009

An experiment is proposed on the coherent quantum dynamics of a semiconductor microcavity containing quantum dots. Modeling the experiment using a generalized Dicke model, we show that a tailored excitation pulse can create an energy-dependent population of excitons, which subsequently evolves to a quantum condensate of excitons and photons. The population is created by a generalization of adiabatic rapid passage and then condenses due to a dynamical analog of the BCS instability.

“…[5][6][7][8][9][10] While these predictions are undoubtedly interesting, more dramatic departures from the physics of equilibrium condensates are seen experimentally. An equilibrium condensate is characterized by a macroscopic occupation at the chemical potential; for a trapped ideal Bose gas, this is the ground-state energy of the trap, while more generally it is the lowest eigenvalue of the Gross-Pitaevskii equation.…”

Section: Introductionmentioning

confidence: 99%

Mode locking and mode competition in a nonequilibrium solid-state condensate

Eastham

2008

A trapped polariton condensate with continuous pumping and decay is analyzed using a generalized GrossPitaevskii model. Whereas an equilibrium condensate is characterized by a macroscopic occupation of a ground state, here the steady states take more general forms. Some are characterized by a large population in an excited state; others by large populations in several states, which may overlap spatially. In the latter case, the highly populated states synchronize to a common frequency above a critical density. At intermediate densities, they can drive condensation in other trap modes by parametric scattering. Estimates for the critical density of the synchronization transition are consistent with experiments.