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SUMMARY:Quantum memories using electron and nuclear spins in the solid sta
 te - Dr John Morton\, Materials Department\, University of Oxford
DTSTART:20110221T141500Z
DTEND:20110221T160000Z
UID:TALK29624@talks.cam.ac.uk
CONTACT:afw24
DESCRIPTION:Electron spins associated with donors in silicon have great po
 tential for applications in quantum technologies due to their extremely lo
 ng coherence times (tens-hundreds of milliseconds)\, ability to be manipul
 ated on a short timescale (tens of nanoseconds)\, and interaction with oth
 er degrees of freedom (such as nuclear spins for memory\, or charge for re
 adout). I shall discuss the use of a coupled donor nuclear spin as a robus
 t coherent memory element for the state of the electron spin [1]. The cohe
 rence lifetime of the 31P quantum memory is studied as a function of donor
  concentration and temperature\, and is found to exceed two seconds at 5.5
 K. I'll discuss the extension of these experiments to other donors in sili
 con\, such as bismuth\, and show how hyperpolarisation of the nuclear spin
  can be used to generated true entanglement between the electron and nucle
 ar spin associated with a P donor\, verified by extracting the density mat
 rix of the two-spin system. [2] \n\nThe large number of spins used in thes
 e experiments is capable of storing a much larger amount of information if
  one uses distributed collective modes\, as in holography. We demonstrate 
 the storage and retrieval of weak 10 GHz coherent excitations in distribut
 ed memories based on donors in silicon\, storing up to 100 weak microwave 
 excitations in a spin ensemble and recalling them sequentially. We also de
 monstrate the storage and retrieval of such multiple excitations into a co
 upled nuclear spin\, for more robust storage [3]. Such experiments could b
 e used towards coupling superconducting qubits to spin ensembles\, via sup
 erconducting resonators [4].\n\n[1] J. J. L. Morton et al.\, Nature 455 10
 85 (2008)\n[2] S. Simmons et al. Nature 470 69 (2011)\n[3] H. Wu et al. Ph
 ys Rev Lett 105 140503 (2010)\n[4] D. Schuster et al. Phys Rev Lett 105 14
 0501 (2010)\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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