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Q: Quantenoptik
Q 12: Quantum Information III
Q 12.2: Talk
Tuesday, April 3, 2001, 16:15–16:30, H 3010
Cryptography with single-photon two-qubit states — •Almut Beige1, Berthold-Georg Englert1,2, Christian Kurtsiefer3, and Harald Weinfurter3 — 1Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching — 2Atominstitut, Technische Universität Wien, Stadionallee 2, 1020 Wien — 3Sektion Physik, Universität München, Schellingstr. 4, 80799 München
We propose a cryptographic scheme in which Alice communicates with Bob by sending him single photons that she prepares in suitably chosen two-qubit states. One qubit is the photon polarization (“vertical” or “horizontal”), the other is a spatial alternative (“in the right fiber” or “in the left fiber”). Under ideal conditions Alice and Bob get a key bit for each photon sent, whereas other schemes [1,2] need at least two photons. Security originates both in a free choice of the two-qubit state sent and in Bob’s random choice of the measurement performed on the photon he receives. An eavesdropper cannot intercept all bits and his presence can be noticed by a significantly increased error rate. An experimental setup that implements the scheme can be realized with the aid of the universal two-qubit gates that where introduced recently [3].
[1] A. Ekert, Phys. Rev. Lett. 67, 661 (1991).
[2] C. H. Bennett, Phys. Rev. Lett. 68, 3121 (1992).
[3] B.-G. Englert, C. Kurtsiefer, and H. Weinfurter, Phys. Rev. A (in press).