Experimental Eavesdropping Based on Optimal Quantum Cloning

TL;DR

This paper experimentally demonstrates how an eavesdropper can use optimal quantum cloning to subtly intercept quantum cryptography signals, potentially compromising security by hiding disturbances within normal transmission noise.

Contribution

The study presents the first experimental implementation of symmetric individual eavesdropping using a high-success-rate quantum cloning device on BB84 and R04 protocols.

Findings

Eavesdropping can be concealed within typical transmission losses.

Optimal quantum cloning enables effective eavesdropping with high success rate.

The experiment highlights potential vulnerabilities in quantum cryptography systems.

Abstract

The security of quantum cryptography is guaranteed by the no-cloning theorem, which implies that an eavesdropper copying transmitted qubits in unknown states causes their disturbance. Nevertheless, in real cryptographic systems some level of disturbance has to be allowed to cover, e.g., transmission losses. An eavesdropper can attack such systems by replacing a noisy channel by a better one and by performing approximate cloning of transmitted qubits which disturb them but below the noise level assumed by legitimate users. We experimentally demonstrate such symmetric individual eavesdropping on the quantum key distribution protocols of Bennett and Brassard (BB84) and the trine-state spherical code of Renes (R04) with two-level probes prepared using a recently developed photonic multifunctional quantum cloner [K. Lemr et al., Phys. Rev. A 85, 050307(R) (2012)]. We demonstrated that our optimal cloning device with high-success rate makes the eavesdropping possible by hiding it in usual transmission losses. We believe that this experiment can stimulate the quest for other operational applications of quantum cloning.