文档介绍：Ultrafast Coherent Dynamics
in Semiconductor Quantum Dots
Han Htoon and Chih-Kang Shih
Department of Physics, University of Texas
Austin TX 78712, USA
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Abstract. In this chapter we will review the studies on ultrafast coherence phe-
nomena of self-assembled semiconductor quantum dots (SAQDs). These studies
provide the understanding required for the utilization of quantum dots as the fun-
damental building block of a solid-state puter. We performed extensive
studies on quantum-decoherence processes of excitons trapped in the various ex-
cited states of SAQDs. Energy-level structure and dephasing times of excited states
were first determined by conducting photoluminescence-excitation spectroscopy and
wavepacket interferometry on a large number of individual SAQDs. Major mech-
anisms responsible for the dephasing of various excited quantum states are deter-
mined through the systematic analysis of the correlation between dephasing times
and energy-level structure of the QDs. The studies revealed that the dephasing
in some of the energetically isolated excited states was strongly suppressed due
to the “phonon bottleneck” effect. These states with long dephasing times further
provide opportunities to explore other fundamental quantum-coherent phenomena.
We observed the direct experimental evidence of Rabi oscillation in these types of
excited states. Furthermore, wavepacket-interferometry experiments performed on
these states in the strong-excitation regime revealed a new type of quantum-inter-
ference phenomenon that emerged from the interplay between quantum interference
and the nonlinear effect of Rabi oscillation. This phenomenon can be utilized as
a coherent controlmechanism where both phase and amplitude of a wavefunction
can be manipulated simultaneously.
1 Introduction
Semiconductor quantum dots (SQDs) are nanometer-scale semiconductor
crystals, where electrons and holes are confined in all three dimensions. This