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Q: Fachverband Quantenoptik und Photonik

Q 52: Quanteninformation: Quantenkommunikation II

Q 52.10: Talk

Thursday, March 5, 2009, 18:45–19:00, Audi-B

Quantum key distribution using phase-shift keying — •Denis Sych and Gerd Leuchs — Max-Planck-Institut für die Physik des Lichts, IOIP, Universität Erlangen-Nürnberg, Günther-Scharowsky-Str. 1, Bau 24, 91058 Erlangen, Deutschland

We report on the detailed analysis of a new protocol for continuous variable quantum key distribution using phase-shift keying. The novelty of the protocol is a multi letter alphabet consisting of coherent states of light with a fixed amplitude and variable phase. Information is encoded in the phase of a coherent state which can be chosen from a regular discrete set consisting, however, of an arbitrary number of letters from two to infinity. Thus our protocol can be regarded as a smooth transition between the protocols based on discrete and continuous modulation of coherent states.

We evaluate the security of the protocol against the beam-splitting and intercept-and-resend attacks. For error correction we consider the direct and reverse reconciliation schemes, both idealized and realistic. We investigate how imperfections of the realistic error correction schemes affect the key rate. As a result we show that the secret key generation rate of the proposed protocol can be of an order higher than that of the binary phase encoding. The optimal parameters (number of letters, amplitude of the signal, and postselection thresholds) are explicitly presented.