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APS » Journals » Phys. Rev. Lett. » Volume 101 » Issue 26
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Phys. Rev. Lett. 101, 260505 (2008) [4 pages]

Experimental Direct Observation of Mixed State Entanglement

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Christian Schmid, Nikolai Kiesel, Witlef Wieczorek, and Harald Weinfurter
Max-Planck-Institute of Quantum Optics, Hans-Kopfermann-Straße 1, 85748 Garching, Germany
Department of Physics, Ludwig-Maximilians-University, Schellingstraße 4, 80799 Munich, Germany

Florian Mintert and Andreas Buchleitner
Institute of Physics, Albert-Ludwigs University of Freiburg, Hermann-Herder-Straße 3, 79104 Freiburg, Germany

Received 15 August 2008; published 31 December 2008

We report on the direct estimation of concurrence for mixed quantum states. The used method relies on joint measurements on two copies of an entangled state. In the experimental demonstration two polarization-entangled photon pairs emitted from spontaneous parametric down-conversion are analyzed together using a linear optics controlled phase gate. We demonstrate that the measured data, without need for further numerical processing, directly yield reliable estimates, despite experimental imperfections.

© 2008 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.101.260505
DOI:
10.1103/PhysRevLett.101.260505
PACS:
03.67.Mn, 42.50.Dv
 
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