Roton entanglement in quenched dipolar Bose-Einstein condensates

Abstract

We study quasi-two-dimensional dipolar Bose-Einstein condensates, in which the Bogoliubov excitation spectrum displays, at sufficiently large gas density, a deep roton minimum due to the spatially anisotropic behavior of the dipolar two-body potential. A rapid quench, performed on the speed of sound of excitations propagating on the condensate background, leads to the dynamical Casimir effect, which can be characterized by measuring the density-density correlation function. It is shown, for both zero and finite initial temperatures, that the continuous-variable bipartite quantum state of the created quasiparticle pairs with opposite momenta, resulting from the quench, displays an enhanced potential for the presence of entanglement (represented by nonseparable and steerable quasiparticle states), when compared to a gas with solely repulsive contact interactions. Steerable quasiparticle pairs contain momenta from close to the roton, and hence quantum correlations significantly increase in the presence of a deep roton minimum.

Fifty Years of the Dynamical Casimir Effect

“…Analogs of the DCE in Bose-Einstein condensates and ultracold gases with time-dependent parameters were considered in [352][353][354][355][356][357][358][359][360][361][362][363][364]. An obvious advantage of replacing EM waves with their sound analogs is a possibility of achieving high ratios of effective velocities to the sound speed, including the supersonic regimes [358,360].…”

“…Various aspects of the problem of entanglement in systems with moving mirrors (or their analogs) were considered in Refs. [143,144,333,346,361,363,[524][525][526][527][528][529][530][531][532][533][534][535][536][537][538][539]. The quantum discord in the DCE was the subject of studies [333,540].…”

Momentum distribution and coherence of a weakly interacting Bose gas after a quench

“…The main advantage of using the relation (25) [instead of (17)] is that it makes it possible to directly relate the expectation values of the observables to the initial distribution of quasiparticles. Besides, when written as functions of U k (t, t 0 ) and V k (t, t 0 ), these relations retain the same form as in the case of time-independent coupling, where the weights are given by the standard Bogoliubov expression.…”

“…(37) only the terms containing two particle operators with nonvanishing momentum (those with just one such operator cannot contribute because of momentum conservation). Then, using the transformation (25), one ends up with…”

Dynamical excitation of maxon and roton modes in a Rydberg-dressed Bose-Einstein condensate

“…In a weakly interacting BEC, the quantum depletion grows exponentially to a steady value ∝ ζ − 1 3 , while oscillatory patterns are not present in the depletion [11], due to the fact that low energy phonon modes dominate the quench dynamics. In dipolar BECs [19,20,24,54,55], on the other hand, roton modes are formed due to the interplay between long-range dipolar and s-wave interactions [19,20,24,54,55]. These roton modes can be excited by quenching the dipolar interaction, while maxon modes are typically C. Quantum depletion in the long time limit…”