Memory Effects in Spin Chain Channels for Information Transmission

TL;DR

This paper explores how memory effects in ferromagnetic spin chain channels influence their capacity for quantum and classical information transmission, revealing that memory can enhance channel performance beyond memoryless limits.

Contribution

It introduces a method to quantify memory effects in spin chain channels and demonstrates how these effects can improve transmission fidelity and capacity.

Findings

Memory effects can increase classical capacity beyond memoryless limits.

Memory can enhance quantum capacity in certain conditions.

A parameter to measure memory influences channel performance.

Abstract

We investigate the multiple use of a ferromagnetic spin chain for quantum and classical communications without resetting. We find that the memory of the state transmitted during the first use makes the spin chain a qualitatively different quantum channel during the second transmission, for which we find the relevant Kraus operators. We propose a parameter to quantify the amount of memory in the channel and find that it influences the quality of the channel, as reflected through fidelity and entanglement transmissible during the second use. For certain evolution times, the memory allows the channel to exceed the memoryless classical capacity (achieved by separable inputs) and in some cases it can also enhance the quantum capacity.