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SUMMARY:Carbon nanotubes as Cooper pair beam splitters - Dr Takis Kontos\,
  Laboratoire Pierre Aigrain\, Ecole Normale Supérieure\, Paris\, France
DTSTART:20110307T141500Z
DTEND:20110307T160000Z
UID:TALK29627@talks.cam.ac.uk
CONTACT:afw24
DESCRIPTION:Quantum optics has been an important source of inspiration for
  many recent experiments in nanoscale electric circuits. One of the basic 
 goals is the generation of entangled electronic states in solid state syst
 ems. Superconductors have been suggested as a natural source of spin entan
 glement\, due to the singlet pairing state of Cooper pairs. One important 
 building block required for the implementation of entanglement experiments
  using superconductors is a Cooper-pair beam splitter which should split t
 he singlet state into two different electronic orbitals. The basic mechani
 sm for converting Cooper pairs into quasiparticles is the Andreev reflecti
 on in which an originally quantum coherent electron pair in the singlet sp
 in state is produced at an interface between a superconductor and a normal
  conductor. Conventional Andreev reflections are local and cannot readily 
 be used to create bipartite states. Many theoretical proposals for circumv
 enting this fact have been around for the last decade. It has been suggest
 ed to make use of electron-electron interactions\, spin filtering or anoma
 lous scattering in graphene to promote Cooper-pair splitting\, i.e.\, the 
 crossed Andreev reflection process. In this work\, we have used Coulomb in
 teractions as well as size quantization in order to favor the crossed Andr
 eev reflection processes in carbon nanotubes\, realizing an efficient Coop
 er pair splitter [1\,2]. The devices studied are double quantum dots which
  can be viewed as artificial molecules connected to one superconducting re
 servoir and two normal reservoirs. Thanks to their tunability\, they allow
  to change in situ the probability of emitting spit Cooper pairs. These fi
 ndings open an avenue for more complex quantum optics like experiments wit
 h electronics sates which should allow\, among other things\, to test the 
 coherence of the emitted split Cooper pairs.\n\n[1] L. G. Herrmann\, F. Po
 rtier\, P. Roche\, A. Levy Yeyati\, T. Kontos\, and C. Strunk Phys. Rev. L
 ett. 104\, 026801 (2010).\n[2] L. Hofstetter\, S. Csonka\, J. Nygard\, and
  C. Schönenberger\, Nature 461\, 960 (2009).\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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