Quantum model for mode locking in pulsed semiconductor quantum dots. (arXiv:1609.06528v3 [cond-mat.mes-hall] UPDATED)

Quantum dots in GaAs/InGaAs structures have been proposed as a candidate
system for realizing quantum computing. The short coherence time of the
electronic quantum state that arises from coupling to the nuclei of the
substrate is dramatically increased if the system is subjected to a magnetic
field and to repeated optical pulsing. This enhancement is due to mode locking:
Oscillation frequencies resonant with the pulsing frequencies are enhanced,
while off-resonant oscillations eventually die out. Because the resonant
frequencies are determined by the pulsing frequency only, the system becomes
immune to frequency shifts caused by the nuclear coupling and by slight
variations between individual quantum dots. The effects remain even after the
optical pulsing is terminated. In this work, we explore the phenomenon of mode
locking from a quantum mechanical perspective. We treat the dynamics using the
central spin model, which includes coupling to 10-20 nuclei and incoherent
decay of the excited electronic state, in a perturbative framework. Using
scaling arguments, we extrapolate our results to realistic system parameters.
We find that the synchronization to the pulsing frequency needs time scales in
the order of 1 s.

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