Experimental quantum cryptography scheme based on orthogonal states

TL;DR

This paper reports an experimental implementation of a quantum cryptography scheme that uses orthogonal states, which can be cloned but still allow eavesdropper detection, challenging traditional assumptions in quantum security.

Contribution

The authors experimentally realize a quantum cryptography protocol based on orthogonal states, demonstrating its feasibility for secure communication.

Findings

Successful experimental demonstration of the orthogonal states protocol

Eavesdropper detection capability confirmed in practice

Potential for practical quantum cryptography using orthogonal states

Abstract

Since, in general, non-orthogonal states cannot be cloned, any eavesdropping attempt in a Quantum Communication scheme using non-orthogonal states as carriers of information introduces some errors in the transmission, leading to the possibility of detecting the spy. Usually, orthogonal states are not used in Quantum Cryptography schemes since they can be faithfully cloned without altering the transmitted data. Nevertheless, L. Goldberg and L. Vaidman [\prl 75 (1995) 1239] proposed a protocol in which, even if the data exchange is realized using two orthogonal states, any attempt to eavesdrop is detectable by the legal users. In this scheme the orthogonal states are superpositions of two localized wave packets travelling along separate channels. Here we present an experiment realizing this scheme.