On the rate of convergence for the mean field approximation of many-body quantum dynamics

TL;DR

This paper investigates the convergence rate of reduced density matrices in many-body quantum dynamics, demonstrating that the $1/n$ rate holds under broader conditions than previously known, including correlated initial states.

Contribution

It extends the known convergence rate results to more general initial states, showing that initial coherence is not essential for the $1/n$ rate in mean field limits.

Findings

The $1/n$ convergence rate applies to correlated initial states.

Initial coherence is not necessary for the convergence rate.

Numerical simulations support the theoretical results.

Abstract

We consider the time evolution of quantum states by many-body Schr\"odinger dynamics and study the rate of convergence of their reduced density matrices in the mean field limit. If the prepared state at initial time is of coherent or factorized type and the number of particles $n$ is large enough then it is known that $1/n$ is the correct rate of convergence at any time. We show in the simple case of bounded pair potentials that the previous rate of convergence holds in more general situations with possibly correlated prepared states. In particular, it turns out that the coherent structure at initial time is unessential and the important fact is rather the speed of convergence of all reduced density matrices of the prepared states. We illustrate our result with several numerical simulations and examples of multi-partite entangled quantum states borrowed from quantum information.