Experimental cheat-sensitive quantum weak coin flipping

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Quantum Communication Networks

Background:

• Quantum networks require cryptographic primitives for security, similar to classical networks.
• Weak coin flipping (WCF) is a crucial primitive enabling mistrustful parties to agree on a random bit with opposing preferences.
• Perfect information-theoretic security is theoretically achievable for quantum WCF.

Purpose of the Study:

• To overcome conceptual and practical challenges hindering experimental demonstration of quantum WCF.
• To experimentally demonstrate cheat sensitivity in quantum WCF, where cheating is detectable and honest parties are not penalized.
• To achieve information-theoretic security for WCF, a feat not known in classical cryptography.

Main Methods:

• Implementation of a refined, loss-tolerant protocol for quantum weak coin flipping.
• Utilization of heralded single photons generated via spontaneous parametric down-conversion.
• Employment of a linear optical interferometer with variable beam splitters and a fast optical switch for verification.

Main Results:

• Successful experimental demonstration of quantum weak coin flipping with cheat sensitivity.
• Maintained high protocol benchmark values even with attenuation simulating several kilometers of telecom fiber.
• Showcased the practical feasibility of a quantum primitive offering unique security guarantees.

Conclusions:

• Quantum resources can enable secure cryptographic primitives like weak coin flipping with enhanced security properties.
• The experimental demonstration overcomes previous limitations, paving the way for secure quantum communication.
• The developed protocol is robust against losses, making it suitable for real-world quantum network applications.