Open dynamics under rapid repeated interaction

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.Comment: 28 pages, 1 figure, RevTeX 4.1. V2: Updated to match published versio

Nonequilibrium dynamics with finite-time repeated interactions

“…For g x = g y = g and ω s = ω p , the system-probe interaction describes a resonant exchange of excitation that preserves the total energy. In other words, the resonant probes realize a channel of thermal operations that effectively models spin thermalization, as often noticed and exploited [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. This holds true for arbitrary system spin numbers J, see App.…”

Gaussian ancillary bombardment

“…To study the general scenario, in Sec. III we adapt the rapid repeated interaction formalism developed in [6,7] to the Gaussian setting. Specifically, we construct an interpolating master equation for the discrete time dynamics induced by the rapid interactions.…”

Collisional Quantum Thermometry

“…In this Letter, we introduce an alternative framework of thermometry inspired by collisional models [23][24][25][26][27], in which the quantum advantages arise from repeated interactions between a continuous stream of independently prepared ancillas and a system mediating the thermal contact with the environment. We show that, at sufficiently high repetition rates and strong interactions, individual ancillas already surpass the thermal Cramer-Rao bound [12].…”