Coherent control of quantum dots

In recent years much effort has been devoted to the use of semiconductor quantum dotsystems as building blocks for solid-state-based quantum logic devices. One importantparameter for such devices is the coherence time, which determines the number ofpossible quantum operations. From earlier measurements the coherence time of the selfassembledquantum dots (QDs) has been reported to be limited by the spontaneousemission rate at cryogenic temperatures1.In this project we propose to alter the coherence time of QDs by taking advantage of arecent technique on modifying spontaneous emission rates with optical nano structures2.As a basis for understanding the change in spontaneous emission rate due to optical nanostructuring, we propose to start by investigating QDs in the close vicinity of a highreflectance mirror. The advantage of this simple system is that the optical mode densitycan be modeled analytically, and it thus serves as a good reference for understandingmore complex systems as e.g., a QD in a microcavity and a QD inside a photonic bandgap structure.We present the current progress in the experiment where we measure spontaneousemission at the single photon level from single QDs. We are currently setting up twoexperiments: One for measuring time-resolved spontaneous emission and one forextracting the linewidth of single QDs. We discuss in detail the theoretical predictions forthe change in spontaneous emission rate for the QD-mirror system. An outlook at moreinvolved nano-structured systems will also be given. 1D. Birkedal, K. Leosson and J.M. Hvam, Phys. Rev. Lett. 87, 227401 (2001) 2P. Lodahl et al, Nature 430, 654-657 (2004)