Coherent control of excitons in quantum dots: A pedegogical introduction

摘要

To conclude, the foregoing treatment considered coherent control of exciton populations in an inhomogeneous distribution of QDs. We considered weak-field coherent control, i.e., the control could be treated in linear optics. Moreover, we considered a simple pulse shape, i.e., a pair of mutually time-delayed phase-locked Gaussian pulses. We found that to γ is necessary for a high degree of coherent control. In addition, for the highest contrast, the probe pulse should have the same center frequency as the pump, and the probe duration should be ～ to. From one viewpoint, the aim was to find control pulses whose spectrum vanished at the signal frequency, but where the spectra of the constituent pulses themselves did not vanish at the signal frequency. In other words, we sought to induce a hole within the spectral hole. For the pulse shapes chosen, a simple sinusoidal modulation overlies the single-pulse spectrum thus producing the hole in the hole. More complicated pulses may also be possible―in particular, pulses for which the hole in the hole is spectrally broader, thus enabling one to use shorter probe pulses. For implementation, however, complex pulse shaping may not be feasible; the double pulses we considered can be simply made by means of a beam splitter and a delay line.