Hannover 2003 – scientific programme

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Q: Quantenoptik

Q 50: Quantenkommunikation

Q 50.1: Talk

Friday, March 28, 2003, 14:00–14:15, F102

Characterising two-party correlations for Quantum Key Distribution — •Marcos Curty and Norbert Lütkenhaus — Quantum Information Theory Group, Zentrum für Moderne Optik, University Erlangen-Nürnberg, Staudtstr. 7/B2, D-91058 Erlangen

In order to construct new practical and efficient Quantum Key Distribution (QKD) protocols it is vital to separate the generation of two-party correlations from the public discussion protocol that generates an unconditional secure key from those data. A necessary condition to make QKD unconditional secure is to establish correlations of quantum-mechanical nature among the legimate users. In order to generate this type of correlations, the QKD protocol has to employ signal states and detection methods such that the observed correlations cannot be explained by an entanglement breaking channel [1]. Intercept-resend attacks are an example of an entanglement breaking channel. In our analysis we employ the so-called entanglement witness formalism [2] to investigate the signal states and detection methods of the BB84 protocol. This approach provides us with practical upper bounds on the performance on QKD schemes. As a special case, we show that for some asymmetric error patterns even for error rates above 25 % the presence of quantum correlations can be demonstrated.

[1] M.B. Ruskai, quant-ph/0207100.

[2] M. Horodecki, P. Horodecki, and R. Horodecki, Phys. Lett. A 223, 1 (1996); B.M. Terhal, Phys. Lett A 271, 319 (2000); M. Lewenstein, B. Kraus, J.I. Cirac, and P. Horodecki, PRA 62, 052310.