Quantum key distribution using intra-particle entanglement

TL;DR

This paper explores using intra-particle entanglement in quantum key distribution to improve security and efficiency, demonstrating that entanglement is necessary but not sufficient for secrecy.

Contribution

It introduces intra-particle entanglement as a practical resource for enhancing BB84 protocol security and analyzes its robustness against simple incoherent attacks.

Findings

States enabling secrecy distillation are entangled.

Intra-particle entanglement can be generated with linear optics.

Security exceeds mere entanglement, indicating stronger conditions are needed.

Abstract

We propose the use of intra-particle entanglement to enhance the security of a practical implementation of the Bennett-Brassard-1984 (BB84) quantum key distribution scheme. Intra-particle entanglement is an attractive resource since it can be easily generated using only linear optics. Security is studied under a simple model of incoherent attack for protocols involving two or all five mutually unbiased bases. In terms of efficiency of secret key generation and tolerable error rate, the latter is found to be superior to the former. We find that states that allow secrecy distillation are necessarily entangled, though they may be local. Since more powerful attacks by Eve obviously exist, our result implies that security is a strictly stronger condition than entanglement for these protocols.