Upper bounds on mixing rates

TL;DR

This paper establishes upper bounds on the rate of change of von Neumann entropy for ensembles of quantum states under non-local unitary evolution, including specific bounds for two-state ensembles and conjectures for general cases.

Contribution

It provides new upper bounds on the mixing rate of quantum ensembles, including a proven bound for two-state ensembles and a conjectured bound related to Shannon entropy for general ensembles.

Findings

Mixing rate bounded by 4√p(1-p) for two-state ensembles.

Conjecture that mixing rate is bounded by Shannon entropy for general ensembles.

Proven dimension-independent upper bound for general ensembles.

Abstract

We prove upper bounds on the rate, called "mixing rate", at which the von Neumann entropy of the expected density operator of a given ensemble of states changes under non-local unitary evolution. For an ensemble consisting of two states, with probabilities of p and 1-p, we prove that the mixing rate is bounded above by 4\sqrt{p(1-p)} for any Hamiltonian of norm 1. For a general ensemble of states with probabilities distributed according to a random variable X and individually evolving according to any set of bounded Hamiltonians, we conjecture that the mixing rate is bounded above by a Shannon entropy of a random variable X. For this general case we prove an upper bound that is independent of the dimension of the Hilbert space on which states in the ensemble act.