Optimal Receiver for Quantum Cryptography with Two Coherent States
Konrad Banaszek, Bs U · 1998
A setup for discriminating between arbitrary two coherent states of a single light mode with the highest success rate allowed by quantum mechanics is presented. Its application to time-multiplexed quantum key distribution is discussed. PACS numbers: 03.67.Dd, 42.50.\\Gammap, 03.65.Bz From the conceptual point of view, the simplest quantum protocol for establishing a cryptographic key is a transmission of a random sequence of two non-orthogonal states [1]. What makes this protocol secure, is the impossibility of discriminating between these two states with certainty. Thus, any attempt of eavesdropping inevitably generates noise in the transmission channel, which can be detected by the communicating parties [2]. A straightforward optical realisation of this protocol is the use of two weak coherent states in an interferometric setup [1,3]. In the two-state protocol, the cryptographic key is constructed from these events, for which the receiving party managed to identify unambiguously the o...