Darmstadt 2008 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 48: Quanteninformation (Quantenkommunikation)

Q 48.2: Talk

Thursday, March 13, 2008, 16:45–17:00, 1B

Quantum Repeaters using Coherent-State Communication — •Peter van Loock — Optical Quantum Information Theory Group, Max Planck Research Group, Institute of Optics, Information and Photonics, Staudtstr. 7/B2, 91058 Erlangen, Germany

We investigate quantum repeater protocols based upon atomic qubit-entanglement distribution through optical coherent-state communication. Various measurement schemes for an optical mode entangled with two spatially separated atomic qubits are considered in order to nonlocally prepare conditional two-qubit entangled states. In particular, generalized measurements for unambiguous state discrimination enable one to completely eliminate spin-flip errors in the resulting qubit states, as they would occur in a homodyne-based scheme due to the finite overlap of the optical states in phase space [1]. As a result, by using weaker coherent states, high initial fidelities can still be achieved for larger repeater spacing, at the expense of lower entanglement generation rates. In this regime, the coherent-state-based protocols start resembling single-photon-based repeater schemes.

[1] P. van Loock, T. D. Ladd, K. Sanaka, F. Yamaguchi, Kae Nemoto, W. J. Munro, and Y. Yamamoto, Phys. Rev. Lett. 96, 240501 (2006).