Unconditional security proof of a deterministic quantum key distribution with a two-way quantum channel

TL;DR

This paper provides a rigorous security proof for a deterministic quantum key distribution protocol with a two-way quantum channel, ensuring unconditional security against general attacks.

Contribution

It offers the first unconditional security proof for a single-photon four-state DQKD protocol with a two-way channel, addressing previous security controversies.

Findings

Security proof against general attacks established

Unconditional security of the protocol demonstrated

Protocol robustness confirmed under realistic conditions

Abstract

In a deterministic quantum key distribution (DQKD) protocol with a two-way quantum channel, Bob sends a qubit to Alice who then encodes a key bit onto the qubit and sends it back to Bob. After measuring the returned qubit, Bob can obtain Alice's key bit immediately, without basis reconciliation. Since an eavesdropper may attack the qubits traveling on either the Bob-Alice channel or the Alice-Bob channel, the security analysis of DQKD with a two-way quantum channel is complicated and its unconditional security has been controversial. This paper presents a security proof of a single-photon four-state DQKD against general attacks.