Solvable model of a generic driven mixture of trapped Bose-Einstein condensates and properties of a many-boson Floquet state at the limit of an infinite number of particles

TL;DR

This paper introduces an exactly solvable model for a driven mixture of Bose-Einstein condensates, analyzing its many-body and mean-field properties, especially in the limit of infinite particles, revealing insights into Floquet states and angular momentum dynamics.

Contribution

It generalizes the harmonic-interaction model to time-dependent driven mixtures and provides explicit solutions for the Floquet wavefunction, quasienergy, and density matrices at infinite particle limit.

Findings

Time-dependent densities per particle match mean-field predictions at infinite particles.

The many-body state remains 100% condensed in the reduced density matrices.

Quasienergy per particle differs from mean-field value unless the relative center-of-mass is unactivated.

Abstract

A solvable model of a periodically-driven trapped mixture of Bose-Einstein condensates, consisting of $N_1$ interacting bosons of mass $m_1$ driven by a force of amplitude $f_{L,1}$ and $N_2$ interacting bosons of mass $m_2$ driven by a force of amplitude $f_{L,2}$, is presented. The model generalizes the harmonic-interaction model for mixtures to the time-dependent domain. The resulting many-particle ground Floquet wavefunction and quasienergy, as well as the time-dependent densities and reduced density matrices, are prescribed explicitly and analyzed at the many-body and mean-field levels of theory for finite systems and at the limit of an infinite number of particles. We prove that the time-dependent densities per particle are given at the limit of an infinite number of particles by their respective mean-field quantities, and that the time-dependent reduced one-particle and two-particle density matrices per particle of the driven mixture are $100\%$ condensed. Interestingly, the quasienergy per particle {\it does not} coincide with the mean-field value at this limit, unless the relative center-of-mass coordinate of the two Bose-Einstein condensates is not activated by the driving forces $f_{L,1}$ and $f_{L,2}$. As an application, we investigate the imprinting of angular momentum and its fluctuations when steering a Bose-Einstein condensate by an interacting bosonic impurity, and the resulting modes of rotations. Whereas the expectation values per particle of the angular-momentum operator for the many-body and mean-field solutions coincide at the limit of an infinite number of particles, the respective fluctuations can differ substantially. The results are analyzed in terms of the transformation properties of the angular-momentum operator under translations and boosts and the interactions between the particles. Implications are briefly discussed.