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Quantum memories using electron and nuclear spins in the solid state

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Electron spins associated with donors in silicon have great potential for applications in quantum technologies due to their extremely long coherence times (tens-hundreds of milliseconds), ability to be manipulated on a short timescale (tens of nanoseconds), and interaction with other degrees of freedom (such as nuclear spins for memory, or charge for readout). I shall discuss the use of a coupled donor nuclear spin as a robust coherent memory element for the state of the electron spin [1]. The coherence lifetime of the 31P quantum memory is studied as a function of donor concentration and temperature, and is found to exceed two seconds at 5.5K. I’ll discuss the extension of these experiments to other donors in silicon, such as bismuth, and show how hyperpolarisation of the nuclear spin can be used to generated true entanglement between the electron and nuclear spin associated with a P donor, verified by extracting the density matrix of the two-spin system. [2]

The large number of spins used in these 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 distributed memories based on donors in silicon, storing up to 100 weak microwave excitations in a spin ensemble and recalling them sequentially. We also demonstrate the storage and retrieval of such multiple excitations into a coupled nuclear spin, for more robust storage [3]. Such experiments could be used towards coupling superconducting qubits to spin ensembles, via superconducting resonators [4].

[1] J. J. L. Morton et al., Nature 455 1085 (2008) [2] S. Simmons et al. Nature 470 69 (2011) [3] H. Wu et al. Phys Rev Lett 105 140503 (2010) [4] D. Schuster et al. Phys Rev Lett 105 140501 (2010)

This talk is part of the Semiconductor Physics Group Seminars series.

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