Memory effects in attenuation and amplification quantum processes

TL;DR

This paper introduces a bosonic quantum memory channel model that captures correlated noise effects in optical processes, revealing regimes of exponentially enhanced or reduced noise correlations affecting channel capacities.

Contribution

The paper presents a new bosonic memory channel model using collective variables, enabling analysis of correlated noise effects and capacity estimation in quantum optical communication.

Findings

Identifies two regimes with exponentially varying noise correlations.

Maps multi-use channels to equivalent single-mode channels for analysis.

Provides insights into how memory effects influence quantum channel capacities.

Abstract

With increasing communication rates via quantum channels, memory effects become unavoidable whenever the use rate of the channel is comparable to the typical relaxation time of the channel environment. We introduce a model of a bosonic memory channel, describing correlated noise effects in quantum-optical processes via attenuating or amplifying media. To study such a channel model, we make use of a proper set of collective field variables, which allows us to unravel the memory effects, mapping the n-fold concatenation of the memory channel to a unitarily equivalent, direct product of n single-mode bosonic channels. We hence estimate the channel capacities by relying on known results for the memoryless setting. Our findings show that the model is characterized by two different regimes, in which the cross correlations induced by the noise among different channel uses are either exponentially enhanced or exponentially reduced.