Frankfurt 2006 – scientific programme

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Q: Quantenoptik und Photonik

Q 58: Quantenkommunikation

Q 58.1: Talk

Thursday, March 16, 2006, 11:10–11:25, HVI

Provable entanglement and security bounds of two-basis QKD protocols using qudits — •Georgios Nikolopoulos and Gernot Alber — Institut für Angewandte Physik, Technische Universität Darmstadt, D-64289 Darmstadt

It has been shown that a necessary precondition for secret key-distillation is that the two legitimate users can prove the presence of entanglement (quantum correlations) in their data. Recently [1], we investigated the values of the average disturbance up to which this condition is satisfied in the context of quantum cryptographic protocols using $d$-level systems. We mainly focused on schemes that use two mutually unbiased bases, thus extending the BB84 quantum key-distribution scheme to higher dimensions. Under the assumption of general coherent attacks, we obtained an analytic expression for the threshold disturbance up to which the two legitimate users of the protocol share provable entanglement. As long as the two legitimate users focus on their sifted key and treat each pair of data independently during the post-processing, our results are valid for arbitrary dimensions. Moreover we investigated the conditions under which an eavesdroper can saturate this theoretical bound, in the context of incoherent and two-qubit coherent attacks [2].

[1] G.M.Nikolopoulos, G.Alber, Phys. Rev. A. 72, 032320 (2005).

[2] G.M.Nikolopoulos, A.Khalique, G.Alber, EPJD (in print).