Abstract

Coherent laser spectroscopy of quantum dots

Brian Gerardot

School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS UK

Strong quantum confinement has led to the observation of discrete, atom-like energy levels in solid-state quantum dots (QDs). However, for a typical self-assembled QD the confinement potential of a particle spans more than 104 atoms. A natural expectation for such a mesoscopic system is that many-body interactions will dominate and lead to unwanted decoherence. In this talk I will present two experiments which confirm that the quantum coherence is in fact maintained for particles in a QD, both for two and three level systems, even with intense optical excitation. In the first example, a single valence-band hole is trapped in the QD. Using a resonant laser, optical pumping of the hole-spin is achieved. Due to a very long spin-relaxation time, high fidelity (~99%) hole-spin preparation is realized. Furthermore, the spin preparation is achieved even when the spin states are degenerate at zero external magnetic field. This verifies that hole spins not only have reduced interactions with phonons but also negligible hyperfine interaction with the nuclear spins of the QD’s constituent atoms. Secondly, I will discuss a two-color pump-probe experiment on the exciton and bi-exciton states in a QD. In the strong-field excitation regime, the dressed-transition states (Autler-Townes splitting) are observed. These results confirm that solid-state mesoscopic systems are a suitable for quantum optical techniques and promising for applications in quantum information processing.