Title: Electron spin dephasing by hyperfine-mediated interactions in a nuclear spin bath

Speaker: Lukasz Cywinski, Condensed Matter Theory Center University of Maryland

Date/Time: Tuesday, February 10, 2009, 1:00 – 2:00 pm

Location: CSRI Building/Room 95 (Sandia-NM)

Brief Abstract: The hyperfine interaction with the nuclear spins is the main source of decoherence of electron spin qubits. While for very large magnetic field B the only decoherence mechanism is spectral diffusion due to dipolar flip-flops of nuclear spins (which influence the electron spin through the hyperfine coupling), with decreasing B the hyperfine-mediated interactions between the nuclear spins become important. These interactions arise from virtual electron-nuclear spin flips leading to coupling between distant nuclei.  I will describe a theory of decoherence which takes advantage of the long-range nature of hyperfine-mediated interaction, and I will present results for pure dephasing decoherence in both Free Induction Decay and Spin Echo settings. For a thermal uncorrelated bath our theory is applicable down to B~10 mT, allowing for comparison with recent experiments in GaAs quantum dots.

CSRI POC: Wayne Witzel, (505) 844-8330