Unconditional Security with Decoherence-Free Subspaces

TL;DR

This paper demonstrates how decoherence-free subspaces can be used to achieve perfectly secure classical communication over quantum channels affected by collective noise, matching the channel's capacity under certain symmetry conditions.

Contribution

It introduces a method for secure classical communication using decoherence-free subspaces in quantum channels, establishing conditions for optimal secrecy rates.

Findings

Decoherence-free subspaces enable perfect secrecy in quantum communication.

The maximum secret communication rate equals the channel's Holevo-Schumacher-Westmoreland capacity under symmetry.

Codes over decoherence-free subspaces act as quantum wiretap channels with zero information gain for eavesdroppers.

Abstract

We show how to use decoherence-free subspaces over collective-noise quantum channels to convey classical information in perfect secrecy. We argue that codes defined over decoherence-free subspaces are codes for quantum wiretap channels in which the gain of information by a non-authorized receiver is zero. We also show that if some symmetry conditions are guaranteed, the maximum rate on which these secret communications take place is equal to the Holevo-Schumacher-Westmoreland capacity of the quantum channel.