Direct and Reverse Secret-Key Capacities of a Quantum Channel

TL;DR

This paper introduces the concepts of direct and reverse secret-key capacities of quantum channels, showing that reverse capacity can be positive even for channels where forward strategies are insecure, especially in continuous variable systems.

Contribution

It defines and analyzes the reverse secret-key capacity of quantum channels, highlighting its positivity in cases where forward strategies fail, particularly for Gaussian channels.

Findings

Reverse secret-key capacity can be positive for antidegradable channels.

Reverse capacity can be achieved with a single feedback classical communication.

The analysis is explicitly demonstrated in the continuous variable Gaussian channel framework.

Abstract

We define the direct and reverse secret-key capacities of a memoryless quantum channel as the optimal rates that entanglement-based quantum key distribution protocols can reach by using a single forward classical communication (direct reconciliation) or a single feedback classical communication (reverse reconciliation). In particular, the reverse secret-key capacity can be positive for antidegradable channels, where no forward strategy is known to be secure. This property is explicitly shown in the continuous variable framework by considering arbitrary one-mode Gaussian channels.