Experimental unconditionally secure bit commitment

TL;DR

This paper reports the experimental realization of unconditionally secure bit commitment using quantum and relativistic principles, demonstrating its feasibility and low cheating probability over long distances.

Contribution

It provides the first experimental implementation of a relativistic quantum bit commitment protocol, confirming its practical security and feasibility.

Findings

Successfully committed bits with less than 5.68×10^-2 cheating probability

Used quantum measurements and free-space optical communication over 20 km

Demonstrated the feasibility of relativistic quantum communication

Abstract

Bit commitment is a fundamental cryptographic task that guarantees a secure commitment between two mutually mistrustful parties and is a building block for many cryptographic primitives, including coin tossing, zero-knowledge proofs, oblivious transfer and secure two-party computation. Unconditionally secure bit commitment was thought to be impossible until recent theoretical protocols that combine quantum mechanics and relativity were shown to elude previous impossibility proofs. Here we implement such a bit commitment protocol. In the experiment, the committer performs quantum measurements using two quantum key distribution systems and the results are transmitted via free-space optical communication to two agents separated with more than 20 km. The security of the protocol relies on the properties of quantum information and relativity theory. We show that, in each run of the experiment, a bit is successfully committed with less than 5.68*10^-2 cheating probability. Our result demonstrates unconditionally secure bit commitment and the experimental feasibility of relativistic quantum communication.