Quantum-locked key distribution at nearly the classical capacity rate

TL;DR

This paper introduces a quantum key distribution protocol leveraging quantum data locking, achieving near-classical capacity rates under certain security assumptions related to the eavesdropper's quantum memory coherence time.

Contribution

It presents a novel protocol for secret key generation over memoryless qudit channels that operates at rates close to the classical capacity, considering practical security criteria.

Findings

Achieves secret key rates close to classical capacity minus one bit for symmetric channels.

Highlights the importance of the accessible information as a security measure with bounded eavesdropper memory.

Demonstrates the protocol's effectiveness on erasure and depolarizing channels.

Abstract

Quantum data locking is a protocol that allows for a small secret key to (un)lock an exponentially larger amount of information, hence yielding the strongest violation of the classical one-time pad encryption in the quantum setting. This violation mirrors a large gap existing between two security criteria for quantum cryptography quantified by two entropic quantities: the Holevo information and the accessible information. We show that the latter becomes a sensible security criterion if an upper bound on the coherence time of the eavesdropper's quantum memory is known. Under this condition we introduce a protocol for secret key generation through a memoryless qudit channel. For channels with enough symmetry, such as the d-dimensional erasure and depolarizing channels, this protocol allows secret key generation at an asymptotic rate as high as the classical capacity minus one bit.