Ergodic Quantum Processes on Finite von Neumann Algebras

TL;DR

This paper investigates ergodic quantum processes on finite von Neumann algebras, demonstrating exponential convergence to replacement channels and analyzing clustering properties of generated states, extending finite-dimensional results to infinite dimensions.

Contribution

It extends the analysis of ergodic quantum processes to infinite-dimensional von Neumann algebras, showing exponential convergence and clustering properties.

Findings

Processes collapse to replacement channels exponentially fast.

Normal states exhibit clustering properties.

Generalizes finite-dimensional ergodic theorems to infinite dimensions.

Abstract

Let $(M,\tau)$ be a tracial von Neumann algebra with a separable predual and let $(\Omega, \mathbb{P})$ be a probability space. A bounded positive random linear operator on $L^1(M,\tau)$ is a map $\gamma : \Omega \times L^1(M,\tau) \to L^1(M,\tau)$ so that $\tau(\gamma_\omega(x)a)$ is measurable for all $x\in L^1(M,\tau)$ and $a\in M$, and $x\mapsto \gamma_\omega(x)$ is bounded, positive, and linear almost surely. Given an ergodic $T\in Aut(\Omega, \mathbb{P})$, we study quantum processes of the form $\gamma_{T^n \omega}\circ \gamma_{T^{n-1}\omega} \circ \cdots \circ \gamma_{T^m\omega}$ for $m,n\in \mathbb{Z}$. Using the Hennion metric introduced in [MS22], we show that under reasonable assumptions such processes collapse to replacement channels exponentially fast almost surely. Of particular interest is the case when $\gamma_\omega$ is the predual of a normal positive linear map on $M$. As an example application, we study the clustering properties of normal states that are generated by such random linear operators. These results offer an infinite dimensional generalization of the theorems in [MS22].