Spin echo of a single electron in a quantum dot

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Date/Time:Thursday, 18 Feb 2010 - Saturday, 20 Feb 2010
Location:Physics 5
Channel:Condensed Matter Physics
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L. Cywinski Institute of Physics, Polish Academy of Sciences, Warsaw, Poland

The problem of the dynamics of an electron spin coupled by a hyperfine (hf) interaction to nuclear spins has been a focus of large theoretical attention, since the interaction with the nuclear bath is the most limiting decoherence mechanism in spin qubits based on quantum dots made of III-V materials. Recently an analytical theory of pure dephasing decoherence of an electron spin hf coupled to the nuclei was put forth [1,2]. This theory takes advangage of long-range character of hf-mediated interactions (which couple remote nuclei via virtual flip-flops with the electron spin), allowing the resummation of the leading terms in an 1/N expansion of the decoherence time-evolution function (N being the large number of nuclear spins interacting appreciably with the electron spin). Such an approach is applicable on a certain time-scale (estimated to be on the order of microseconds for large GaAs dots), and for magnetic fields much larger than the typical Overhauser field fluctuation. However, a more precise investigation of limits of applicaibillity and accuracy of this theory is required. I will discuss the theoretical predictions for spin echo decay (for which there are experimental results with which comparisons can be made) obtained both with the approximate analytical approach, and by exact numerical simulations of a system of geq 20 nuclei. With the latter method the regime of very low magnetic fields can also be investigated, and I will discuss new and unpublished results obtained there.

[1]. L. Cywinski, W.M. Witzel, and S. Das Sarma, Phys. Rev. Lett. 102, 057601 (2009).
[2]. L. Cywinski, W.M. Witzel, and S. Das Sarma, Phys. Rev. B 79, 245314 (2009).