Single-Photon Advantage in Quantum Cryptography Beyond QKD

TL;DR

This paper demonstrates a quantum strong coin flipping protocol using single-photon states, showing a clear advantage over classical methods and faint laser pulse implementations, advancing quantum cryptography towards practical complex tasks.

Contribution

It experimentally implements a single-photon quantum coin flipping protocol with a deterministic quantum dot source, surpassing classical and faint laser pulse methods.

Findings

Achieved quantum advantage with single-photon states in coin flipping

Utilized a deterministic quantum dot light source for low error rates

Paved the way for complex cryptographic tasks in quantum internet

Abstract

Quantum key distribution (QKD) can be used to establish a secret key between trusted parties. Many practical use-cases in communication networks, however, involve parties who do not trust each other. A fundamental cryptographic building block for such distrustful scenarios is quantum coin flipping, which has been investigated only in few experimental studies to date, all of which used probabilistic quantum light sources imposing fundamental limitations. Here, we experimentally implement a quantum strong coin flipping protocol using single-photon states and demonstrate a quantum advantage compared to both classical realizations and implementations using faint laser pulses. We achieve this by employing a state-of-the-art deterministic quantum dot light source in combination with fast, random polarization-state encoding enabling sufficiently low quantum bit error ratio. By demonstrating a single-photon quantum advantage in a cryptographic primitive beyond QKD, our work represents a major advance towards the implementation of complex cryptographic tasks in a future quantum internet.