No information flow using statistical fluctuations, and quantum cryptography

Abstract

The communication protocol of Home and Whitaker [Phys. Rev. A 67, 022306 (2003)] is examined in some detail, and found to work equally well using a separable state. The protocol is in fact completely classical, based on simple post-selection of suitable experimental runs. The quantum cryptography protocol proposed in the same publication is also examined, and is found to indeed need quantum properties for the system to be secure. However, the security test proposed in the mentioned paper is found to be insufficient, and a modification is proposed here that will ensure security.