Experimental cheat-sensitive quantum weak coin flipping

TL;DR

This paper demonstrates an experimental quantum weak coin flipping protocol that is cheat-sensitive, loss-tolerant, and maintains security over several kilometers of optical fiber, advancing quantum cryptography capabilities.

Contribution

It provides the first practical implementation of cheat-sensitive quantum weak coin flipping with loss tolerance and real-world optical fiber deployment.

Findings

Achieved cheat sensitivity in quantum coin flipping.

Maintained high protocol performance over kilometers of optical fiber.

Demonstrated loss-tolerant quantum cryptographic protocol in practice.

Abstract

As in modern communication networks, the security of quantum networks will rely on complex cryptographic tasks that are based on a handful of fundamental primitives. Weak coin flipping (WCF) is a significant such primitive which allows two mistrustful parties to agree on a random bit while they favor opposite outcomes. Remarkably, perfect information-theoretic security can be achieved in principle for quantum WCF. Here, we overcome conceptual and practical issues that have prevented the experimental demonstration of this primitive to date, and demonstrate how quantum resources can provide cheat sensitivity, whereby each party can detect a cheating opponent, and an honest party is never sanctioned. Such a property is not known to be classically achievable with information-theoretic security. Our experiment implements a refined, loss-tolerant version of a recently proposed theoretical protocol and exploits heralded single photons generated by spontaneous parametric down conversion, a carefully optimized linear optical interferometer including beam splitters with variable reflectivities and a fast optical switch for the verification step. High values of our protocol benchmarks are maintained for attenuation corresponding to several kilometers of telecom optical fiber.