Nonclassical dynamics of Bose condensates in an optical lattice in the superfluid regime

TL;DR

This paper investigates the non-equilibrium dynamics of a Bose condensate in an optical lattice, revealing how sudden parameter changes induce a transition from superfluid to insulating states, with a novel superposition state description.

Contribution

It introduces a new superposition state framework for nonadiabatic condensate dynamics and demonstrates the inadequacy of standard equations in describing these processes.

Findings

System falls into a far-from-equilibrium state after nonadiabatic process

Superfluid order parameter is a superposition of Glauber coherent states

System loses coherence and becomes insulating during evolution

Abstract

A condensate in an optical lattice, prepared in the ground state of the superfluid regime, is stimulated first by suddenly increasing the optical lattice amplitude and then, after a waiting time, by abruptly decreasing this amplitude to its initial value. Thus the system is first taken to the Mott regime and then back to the initial superfluid regime. We show that, as a consequence of this nonadiabatic process, the system falls into a configuration far from equilibrium whose superfluid order parameter is described in terms of a particular superposition of Glauber coherent states that we derive. We also show that the classical equations of motion describing the time evolution of this system are inequivalent to the standard discrete nonlinear Schreodinger equations. By numerically integrating such equations with several initial conditions, we show that the system loses coherence, becoming insulating.