Repeatable quantum memory channels

TL;DR

This paper introduces the concept of repeatability in quantum memory channels, demonstrating that certain channels like random unitary channels can be implemented repeatedly, unlike nonunital channels.

Contribution

It defines the notion of repeatability for quantum channels and characterizes which channels can be implemented repeatedly using a memory device.

Findings

Random unitary channels are repeatable.

Nonunital channels are not repeatable.

Abstract

Within the framework of quantum memory channels we introduce the notion of repeatability of quantum channels. In particular, a quantum channel is called repeatable if there exist a memory device implementing the same channel on each individual input. We show that random unitary channels can be implemented in a repeatable fashion, whereas the nonunital channels cannot.