Loss-tolerant quantum secure positioning with weak laser sources

TL;DR

This paper introduces a loss-tolerant quantum secure positioning protocol that remains secure under high channel loss, surpassing previous limits, and is practical with weak laser sources.

Contribution

It proposes a novel time-reversed entanglement swapping QPV protocol that is secure against LOCC adversaries regardless of channel loss, even with weak laser sources.

Findings

Secure against LOCC adversaries for any loss with ideal sources

Maintains security with weak laser sources up to 47 dB loss

Overcomes the 3 dB loss limit of previous protocols

Abstract

Quantum position verification (QPV) is the art of verifying the geographical location of an untrusted party. Recently, it has been shown that the widely studied Bennett & Brassard 1984 (BB84) QPV protocol is insecure after the 3 dB loss point assuming local operations and classical communication (LOCC) adversaries. Here, we propose a time-reversed entanglement swapping QPV protocol (based on measurement-device-independent quantum cryptography) that is highly robust against quantum channel loss. First, assuming ideal qubit sources, we show that the protocol is secure against LOCC adversaries for any quantum channel loss, thereby overcoming the 3 dB loss limit. Then, we analyze the security of the protocol in a more practical setting involving weak laser sources and linear optics. In this setting, we find that the security only degrades by an additive constant and the protocol is able to verify positions up to 47 dB channel loss.