Regensburg 2016 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 26: Quantum Dots and Wires: Quantum Optics I

HL 26.1: Hauptvortrag

Dienstag, 8. März 2016, 09:30–10:00, H16

Exploring spin quantum state decoherence in optically active quantum dots — •Jonathan Finley — Walter Schottky Institut and Physik Department, Technische Universität München, Am Coulombwall 4, 85748 Garching, Germany

For spin qubits in optically active quantum dots (QDs) considerable progress has been made in uncovering the qubit dynamics in external magnetic fields (B_ext≥ 50 mT). In contrast, decoherence at B_ext∼ 0T and specifically the role of quadrupolar coupling of nuclear spins is comparatively poorly understood. Phenomenological models of decoherence typically include two basic types of spin relaxation: fast dephasing due to static but randomly distributed hyperfine fields (∼ 2ns) and a much slower process (≥ 1µs) of irreversible monotonic relaxation due either to nuclear spin co-flips or many-body interaction effects. Our results show that electron spin relaxation is determined by three rather than two distinct stages (1). The additional stage corresponds to the effect of coherent precession processes that occur in the nuclear spin bath itself, leading to a relatively fast but incomplete non-monotonic relaxation at intermediate timescales and vanishing exernal magnetic fields (∼750 ns). The interplay between field induced electron spin motion and the quadrupolar induced dynamics of the nuclear field are probed using spin echo. Moreover, we show how new information about spin dynamics can be obtained from direct measurements of two-time spin time correlators (g³(τ₁,τ₂)).(2,3) - Refs: (1) A. Bachtold et al., Nature Physics (2015). DOI: 10.1038/nphys3470, (2) A. Bechtold et al. arXiv:1511.03684, (3) R. B. Liu et al, New. J. Phys, 12 013018, (2010)