Browsing by Author "Chen, Y. N."

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Decoherence of a charge qubit embedded inside a suspended phonon cavity
(2008-01-01)
Liao, Y. Y.
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Chen, Y. N.
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Chou, W. C.
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Chuu, D. S.
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電子物理學系
This study elucidates the theory of phonon-induced decoherence of a double dot charge qubit that is embedded inside a suspended semiconductor slab. The influences of the lattice temperature, width of the slab, and positions of the dots on the decoherence are analyzed. Numerical results indicate that the decoherence in the slab system is weaker than that in a bulk environment. In particular, the decoherence is markedly suppressed by the inhibition of the electron-phonon coupling. Such a system with low decoherence may be useful for manipulating the qubits.
Development of flucytosine resistance in Candida tropicalis due to Loss-of-heterozygosity of FCY2
(2012-06-01)
Chen, Y. N.
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Lo, H. J.
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Wu, C. C.
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Chang, T. P.
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Yang, Y. L.
Electron transport of a driven three-level system in an asymmetric double quantum dot irradiated by an external field
(2007-03-01)
Liao, Y. Y.
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Chuu, D. S.
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Chen, Y. N.
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電子物理學系
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Department of Electrophysics
Electron tunneling through a three-level system in an asymmetric double quantum dot irradiated by an external field is investigated. For a resonant external field, two symmetric peaks occur in the current spectrum. If the field frequency is detuned, unequal contributions from two channels lead to two asymmetric peaks with population inversion, which can be observed with increasing Rabi frequency. On the other hand, as the ground states in two dots are equal, a suppression of current occurs around the resonant frequency. In contrast, an enhanced behavior is found for the case of unequal ground states.
Fluorescence signals of quantum dots influenced by spatially controlled array structures
(2009-10-14)
Chou, J. W.
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Lin, K. C.
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Tang, Y. T.
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Hsueh, F. K.
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Lee, Yao-Jen
Fluorescence signals of quantum dots (QDs) influenced by different array structures of gold-coated silicon nanorods (SiNRs) were investigated via experimental observations and two-dimensional (2D) finite element method (FEM) simulations. On the densest gold-coated SiNRs array structure, the highest QD fluorescence quenching rates were observed and on the sparsest array structure, the highest QD fluorescence enhancement rates were observed. By developing a new technique which obtains the optical image of the array structures without losing information about the QD locations, we were able to further investigate how the QD fluorescence is influenced by spatially controlled array structures.
Photoinduced fluorescence enhancement in colloidal CdSeTe/ZnS core/shell quantum dots
(2008-05-05)
Yuan, C. T.
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Chou, W. C.
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Chuu, D. S.
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Chen, Y. N.
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Lin, C. A.
Photoinduced fluorescence enhancement (PFE) in colloidal CdSeTe/ZnS core/shell quantum dots (QDs) was investigated by monitoring ensemble fluorescence and single-QD fluorescence blinking behavior upon illumination. Ensemble fluorescence was increased in air and in vacuum with different enhanced factors. At the single-QD levels, fluorescence was also enhanced for some individual QDs. Relatively long on times, high quantum yields within the on times, and multilevel on states were found in fluorescence time traces. We suggest that the PFE origin from single-QD viewpoint is attributed to the contributions of surface passivation by photoinduced charged carriers and the formation of neutral core/charged shell QD states. (C) 2008 American Institute of Physics.
Quantum-dot exciton dynamics with a surface plasmon: Band-edge quantum optics
(2009-03-01)
Chen, Y. N.
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Chen, G. Y.
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Chuu, D. S.
;
Brandes, T.
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電子物理學系
We examine the spontaneous emission of a two-level emitter, quantum-dot exciton, into surface plasmons propagating on the surface of a cylindrical nanowire. The numerically obtained dispersion relations are found to influence the spontaneous emission rate strongly. At certain values of the exciton band gap, the emission rates can go to infinity due to the band-edge feature of the dispersion relations. Borrowing the idea from the photonic crystals, we model the quantum-dot exciton dynamics with a non-Markovian way and demonstrate that the decay can undergo an oscillatory behavior. In addition, we also show that the remote entangled states can be generated via super-radiance by using the one-dimensional propagating feature of the nanowire surface plasmons.
Studies on the electronic and vibrational states of colloidal CdSe/ZnS quantum dots under high pressures
(2007-05-09)
Yuan, C. T.
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Lin, Y. C.
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Chen, Y. N.
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Chiu, Q. L.
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Chou, W. C.
The electronic and vibrational states of colloidal core/shell CdSe/ZnS quantum dots are studied at room temperature by using high pressure optical measurements. Pressure-induced quadratic variations of lattice constants can be observed clearly from both photoluminescence ( PL) and Raman spectra up to similar to 7 GPa. This quadratic relationship is consistent with the theoretical prediction. The pressure coefficients of linear and quadratic terms are 32 meV GPa(-1), -1 meV GPa(-2) for PL and 4.2 cm(-1) GPa(-1), -0.1 cm(-1) GPa(-2) for Raman measurements, respectively.