Open dynamics under rapid repeated interaction

TL;DR

This paper explores how rapid repeated quantum interactions with ancillary systems lead to emergent open system dynamics, including decoherence, thermalization, and purification, with bounds on decoherence rates and links to interaction unpredictability.

Contribution

It provides a comprehensive theoretical framework for understanding open quantum dynamics under rapid repeated interactions, extending previous models and deriving bounds on decoherence.

Findings

Decoherence appears as a subleading effect in rapid repeated interactions.

A bound on decoherence rates is derived in this regime.

Various phenomena like projection, thermalization, and dephasing can emerge from the model.

Abstract

We investigate the emergent open dynamics of a quantum system that undergoes rapid repeated unitary interactions with a sequence of ancillary systems. We study in detail how decoherence appears as a subleading effect when a quantum system is 'bombarded' by a quick succession of ancillas. In the most general case, these ancillas are a) taken from an ensemble of quantum systems of different dimensions, b) prepared in different states, and c) interacting with the system through different Hamiltonians. We derive an upper bound on decoherence rates in this regime, and show how a rich variety of phenomena in open dynamics (such as projection, thermalization, purification, and dephasing) can emerge out of our general model of repeated interaction. Furthermore, we show a fundamental link between the strength of the leading order dissipation and the intrinsic "unpredictability" in the system-ancilla interaction. We also discuss how these results encompass and extend results obtained with other earlier models of repeated interaction.