Coherent spectroscopy on single QDs

Quantum dots (QD) have been considered promising candidates for
applications in quantum information processing for a long time. Further
more, they also offer new insight into the fundamental interactions
between a single wavefunction and the semiconductor environment. In both
areas the relaxation and decoherence time scales play a central role.
For quantum information processing long relaxation and coherence times
are essential. For a better understanding of the
semiconductor-wavefunction interactions, the dependency of relaxation
and decoherence times on parameters like magnetic and electric fields
are needed. There is still a vast amount of unanswered fundamental
questions, both experimentally and theoretically.

In this seminar I will introduce coherent spectroscopy on single QDs.
This concept is based on the direct detection of the homodyne field
between a QD and a resonant laser. An extended experimental setup will
also allow readout of resonantly created states, collection of the so
called resonance fluorescence. Resonant spectroscopy will then be
applied to study the relaxation and decoherence times of single hole
spin states confined to a QD. Both, relaxation and decoherence times
show very promising results. Especially a coherence time of around one
microsecond reveals a fundamental difference to electron spin states.
Resonance fluorescence will be demonstrated on a negatively charged
exciton, realising another bullet point on the roadmap to quantum
information processing.