Regensburg 2016 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 25: Quantum Information Systems (Joint session of HL and TT, organized by HL)

HL 25.5: Vortrag

Dienstag, 8. März 2016, 10:30–10:45, H15

A model for slow decoherence in semiconductor quantum dots — •Wouter Beugeling, Frithjof B. Anders, and Götz S. Uhrig — Lehrstuhl für Theoretische Physik I/II, Technische Universität Dortmund, 44221 Dortmund, Germany

Quantum dots on semiconductor materials have been proposed as candidates for quantum computational applications. The information is carried by a single electron spin, which interacts with the substrate nuclei with a hyperfine coupling. The electron spin is manipulated with excitation by periodic laser pulses and by an external magnetic field. The nuclear spins can be polarized indirectly, due to the hyperfine coupling, an effect known as dynamical nuclear polarization.

The leading contribution in the dynamics is the Larmor precession, which dephases due to small frequency shifts from the hyperfine coupling. Typically, the dephasing causes almost complete decoherence at the time scale of the pulse interval. Thus, a different mechanism must be responsible for the finite coherence observed in experiments.

In this presentation, we propose a mechanism explaining the experimental findings. We study the dynamics using the Lindblad equation, which includes the non-unitarity from the decay of the excited state. We separate the time scales of the Larmor precession (fast) and the nuclear-spin dynamics (slow) by treating the hyperfine couplings in a perturbative fashion. We find low-frequency contributions that dephase at a much slower rate, providing a plausible explanation for the finite coherence at the pulse interval time. We support this claim with analytical derivations and numerical results.