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Reducing decoherence of the confined exciton state in a quantum dot by pulse-sequence control
We study the phonon-induced dephasing of the exciton state in a quantum dot
excited by a sequence of ultra-short pulses. We show that the multiple-pulse
control leads to a considerable improvement of the coherence of the optically
excited state. For a fixed control time window, the optimized pulsed control
often leads to a higher degree of coherence than the control by a smooth single
Gaussian pulse. The reduction of dephasing is considerable already for 2-3
pulses.Comment: Final version (moderate changes
Fractal Spectrum of a Quasi_periodically Driven Spin System
We numerically perform a spectral analysis of a quasi-periodically driven
spin 1/2 system, the spectrum of which is Singular Continuous. We compute
fractal dimensions of spectral measures and discuss their connections with the
time behaviour of various dynamical quantities, such as the moments of the
distribution of the wave packet. Our data suggest a close similarity between
the information dimension of the spectrum and the exponent ruling the algebraic
growth of the 'entropic width' of wavepackets.Comment: 17 pages, RevTex, 5 figs. available on request from
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