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Q: Quantenoptik
Q 223: Quantum Information II
Q 223.6: Talk
Tuesday, March 5, 2002, 17:45–18:00, HS 11/215
Multiphoton entanglement — •Manfred Eibl1, Mohamed Bourennane2, Sascha Gaertner2, Nikolai Kiesel2, Christian Kurtsiefer2, and Harald Weinfurter1,2 — 1Max-Planck-Institut für Quantenoptik, Hans-Kopfermannstr.1, 85748 Garching b. München — 2Ludwig-Maximilians-Universität München, Sektion Physik, Schellingstr.4/III, 80799 München
Multiphoton entanglement is the basis of many quantum communication schemes, quantum cryptographic protocols and fundamental tests of quantum theory. Spontaneous parametric down-conversion is the most effective source for polarization entangled photon pairs, and more recently, also for observing 3- and 4-photon entangled states via fragile interferometric set-ups.
Here we show, that a highly entangled 4-photon state can be directly created by parametric downconversion. By pumping the down-conversion crystal with frequency doubled fs pulses from a Ti:Sapphir-laser, we generate a superposition state of a 4-photon GHZ-state and a product of two EPR-states, which shows strong correlations for various sets of analyzer angles. We present a detailed study of the dependency of the various 2- and 4-photon quantum correlations on the bandwidth of the down-conversion photons, and describe how this state can be used for the implementation of novel quantum communication schemes like 4-party secret sharing and quantum telecloning. We finally report on possibilities for the experimentally realization of a 3-photon entangled state, the so called W-state, and discuss some of its properties.