On the general principle of the mean-field approximation for many-boson dynamics

TL;DR

This paper proves the accuracy of mean-field approximation for many-boson dynamics using Wigner measures, under general conditions on the Hamiltonian and initial states, with a focus on uniqueness of solutions in infinite dimensions.

Contribution

It provides a general proof of mean-field approximation validity for many-boson systems using Wigner measures, relaxing model-specific assumptions.

Findings

Mean-field approximation is accurate under specified conditions.

Convergence described via Wigner measures for large particle numbers.

Uniqueness of solutions in infinite-dimensional Liouville equations is crucial.

Abstract

The mean-field approximations of many-boson dynamics are known to be effective in many physical relevant situations. The mathematical justifications of such approximations rely generally on specific considerations which depend too much on the model and on the initial states of the system which are required to be well-prepared. In this article, using the method of Wigner measures, we prove in a fairly complete generality the accuracy of the mean-field approximation. Roughly speaking, we show that the dynamics of a many-boson system are well approximated, in the limit of a large number of particles, by a one particle mean-field equation if the following general principles are satisfied: $\bullet$ The Hamiltonian is in a mean-field regime (i.e.: The interaction and the free energy parts are of the same order with respect to the number of particles). $\bullet$ The interaction is relatively compact with respect to a one particle and it is dominated by the free energy part. $\bullet$ There exists at most one weak solution for the mean-field equation for each initial condition.The convergence towards the mean field limit is described in terms of Wigner (probability) measures and it holds for any initial quantum states with a finite free energy average. The main novelty of this article lies in the use of fine properties of uniqueness for the Liouville equations in infinite dimensional spaces.