Dresden 2017 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 22: Transport: Quantum Coherence and Quantum Information Systems - Theory (jointly with MA, HL)

TT 22.9: Talk

Tuesday, March 21, 2017, 11:45–12:00, HSZ 103

Theory of mode locking in pulsed semiconductor quantum dots — •Wouter Beugeling, Götz S. Uhrig, and Frithjof B. Anders — Lehrstuhl für Theoretische Physik 1/2, TU Dortmund, Dortmund, Germany

Electron spins in semiconductor quantum dots appear unsuitable for quantum computing at first sight, due to their fast decoherence caused by hyperfine interactions to the nuclear spins in the substrate. However, the coherence time is dramatically increased by periodic optical pulsing. The underlying mechanism is known as mode locking: Oscillation frequencies incommensurate with the pulse repetition rate are suppressed, and only resonant contributions remain. Because the resonant frequencies are set by the pulse repetition rate only, the system becomes effectively immune to perturbations induced by the hyperfine interactions and by variations between the individual quantum dots in an ensemble.

In this presentation, we explore the mechanism of mode locking with a combination of analytical and numerical methods. Exploiting the fact that the hyperfine interaction is small compared to the external magnetic field, we calculate the dynamics perturbatively. The resulting frequency distributions show clear signs of mode locking. We study the positions of the resonant frequencies and the rate at which mode locking sets in, and compare the results to other theoretical and experimental studies. We also discuss the influence of the hyperfine coupling strength, of the Zeeman effect of the nuclear spins, and of the pulse shape and detuning.