Associate professor, Department of Applied Physics, Hokkaido University
Quantum mechanical control of quantum dots by using coherently controlled light
One of the fascinating characteristics of quantum dots is their atomic-like discrete density of states with large energy-level spacing, in which acoustic phonon-mediated scattering should be suppressed compared with higher-dimensional structures. As a consequence, excitons in quantum dots are expected to exhibit long coherence time, which is advantageous for application of quantum information processing. In such quantum logic devices, it is important to coherently control quantum units individually.
Our research aims at quantum mechanical control of exciton wavefunctions by using coherently controlled light. Because laser light exhibits high coherence, we can easily manipulate its waveform by a dispersion-free 4-f optical system in conjunction with a spatial light modulator (SLM), which alters the spectral phase of the pulse. By optimizing the excitation pulse, we can address the exciton wavefunctions in individual self-assembled quantum dots (SAQDs).
We here used the sample of SAQDs. In a photoluminescence (PL) spectrum of the sample, several sharp emission lines originating from different SAQDs are observed. For the selective excitation, we optimized the excitation pulse based on the photoluminescence excitation (PLE) resonances. A contour plot of the PL spectra as a function of the phase of SLM shows normalized PL intensities at two peaks with fitting of the data by a sinusoidal function. Both peaks show oscillatory behavior as a consequence of the quantum interference of the wavefunctions in each excited states. Furthermore we can address the exciton wavefunctions even in the collective excitation. This indicates the feasibilities for selective coherent control of individual exciton wavefunctions.
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| Fig. 1 Large Image |
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| (a) Schematic diagram of exciton states in quantum dot. (b) PL and corresponding PLE spectra of self-assembled quantum dots within the same area. |
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| Fig. 2 Large Image |
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| (a) Contour plot of PL intensities of the peak A and B in Fig. 1 (b) at different phase of SLM. (b) Plots of PL intensities with sinusoidal fitting curve. |
Relevant papers
- 1. Koga, T., Nitta, J., Akazaki, T. & Takayanagi, H.
Rashba spin-orbit coupling probed by the weak antilocalization analysis in InAlAs/InGaAs/InAlAs quantum wells as a function of quantum well asymmetry.
Phys. Rev. Lett. 88, 126601 (2002). - 2. Koga, T., Nitta, J. Takayanagi, H. & Datta, S.
Spin-filter device based on the Rashba effect using a non-magnetic resonant tunneling diode.
Phys. Rev. Lett. 89, 046801 (2002).
