Memory effects in quantum channel discrimination

TL;DR

This paper investigates quantum-memory assisted protocols for channel discrimination, establishing their necessity for memory channels and introducing a new distance measure, while also identifying scenarios where they are unnecessary.

Contribution

It introduces the concept of memory-assisted protocols for quantum channel discrimination and defines a new distance measure for channels with memory, highlighting when such protocols are essential.

Findings

Memory-assisted protocols are necessary for optimal discrimination of memory channels.

A new distance measure for channels with memory is proposed.

Memory-assisted protocols are not required for optimal discrimination of certain unitary channels.

Abstract

We consider quantum-memory assisted protocols for discriminating quantum channels. We show that for optimal discrimination of memory channels, memory assisted protocols are needed. This leads to a new notion of distance for channels with memory. For optimal discrimination and estimation of sets of unitary channels memory-assisted protocols are not required.