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SUMMARY:High-fidelity entanglement between a quantum dot spin and a single
  photon via time-resolved downconversion to telecom wavelength - Kristiaan
  De Greve (Stanford University)
DTSTART:20130927T100000Z
DTEND:20130927T113000Z
UID:TALK47043@talks.cam.ac.uk
CONTACT:6270
DESCRIPTION:Kristiaan De Greve1*\, Peter L. McMahon1\, Leo Yu1\, Jason S. 
 Pelc1\, Chandra M. Natarajan1\,4\, David Press1\, Na Young Kim1\, Eisuke A
 be1\,2\, Dirk Bisping3\, Sebastian Maier3\, Christian Schneider3\, Martin 
 Kamp3\, Sven Höfling1\,3\, Robert H. Hadfield4\, Alfred Forchel3\, M. M. 
 Fejer1 & Yoshihisa Yamamoto1\,2\n\n1E. L. Ginzton Laboratory\, Stanford Un
 iversity\, Stanford\, California 94305\, USA\n2National Institute of Infor
 matics\, Hitotsubashi 2-1-2\, Chiyoda-ku\, Tokyo 101-8403\, Japan\n3Techni
 sche Physik\, Physikalisches Institut\, Wilhelm Conrad Röntgen Research C
 enter for Complex Material Systems\, Universität Würzburg\, Am Hubland\,
  D-97074 Würzburg\, Germany\n4School of Engineering\, University of Glasg
 ow\, Glasgow\, G12 8QQ\, United Kingdom\n*Currently at Harvard University\
 , department of Physics\, 11 Oxford Street\, Cambridge MA 02138\, USA\n\nE
 ntanglement between light and matter is at the heart of many quantum commu
 nication schemes that involve built-in quantum memories (such as quantum r
 epeaters). In this presentation\, I will demonstrate recent results involv
 ing entanglement between a single photon and an electron spin qubit in an 
 InAs quantum dot1\,2\,3\,4. \n\nWe developed a time-resolved frequency con
 version technique5\,6 that allows measurement of the arrival time of  sing
 le photon with few-ps timing resolution. With this tool\, we can perform s
 troboscopic measurements of the phase evolution of frequency-superposed ph
 otons\, or\, alternatively\, quantum erase frequency-which-path informatio
 n in polarization- and frequency-entangled photons.\n\nApplying this techn
 ique to the case of spin-photon entanglement in InAs quantum dots6\,7\, we
  obtain a lower bound of the entanglement fidelity of 92%\, still limited 
 by the timing resolution of the frequency conversion. In addition\, the pu
 mp pulses in the conversion tool were chosen to yield converted photons at
  1550 nm\, which is the lowest-loss wavelength for fiber communication\, a
 nd the internal quantum efficiency of the process is well over 70%. CW imp
 lementations of the conversion technique should therefore be able to help 
 in extending the distance between adjacent nodes in quantum repeaters.\n\n
 \nReferences:\n\n1D. Press\, T. Ladd et al\, Nature 456\, 218 (2008)\n2J. 
 Berevosky\, M. Mikkelsen et al.\, Science 320\, 349 (2008)\n3D. Press\, K.
  De Greve et al\, Nat. Phot. 4\, 367 (2010)\n4K. De Greve\, P. McMahon et 
 al\, Nature Physics 7\, 872 (2011)\n5J. S. Pelc\, L. Yu et al\, Opt. Expre
 ss 20\, 27510 (2012)\n6K. De Greve\, L. Yu et al\, Nature 491\, 421 (2012)
 \n7K. De Greve\, P. McMahon et al\, Nature Commun. 4\, 2228 (2013)\n
LOCATION:Rutherford building\, Seminar Room B
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