Browsing by Author "Wijers, C. M. J."

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A hybrid model for the magneto-optics of embedded nano-objects
(2006)
Wijers, C. M. J.
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Voskoboynikov, O.
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Liu, J. L.
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
The influence of the surrounding semiconducting matrix upon the polarizability of embedded nano-objects (nano-rings) has been investigated using a hybrid discrete/continuum model. It describes embedded systems by excess discrete dipoles with excess polarizability against a uniform background with the host material dielectric constant. The polarizability combines the static polarizability of an ellipsoidal ring with a dynamic quantum mechanical frequency dependent term. The result of the model for the particular nano-ring host combination investigated is an increased internal reflectance and an overall strong increment of the structure in reflectance/ellipsometric angles, displaying clearly the optical Aharonov-Bohm effect. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Magnetic Qubit in a Non-Magnetic Semiconductor Quantum Dot Molecule
(2010-09-01)
Voskoboynikov, O.
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Wijers, C. M. J.
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交大名義發表
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National Chiao Tung University
We consider a system of two vertical lens-shaped circular InAs/GaAs quantum dots when an external magnetic field is applied along the system's growth direction. The quantum dots have substantially different diameters in contrast to most of the known systems. We discuss a possibility to coherently drive coupled electronic ground states (to relocate electronic wave functions from one dot to another). This can be described as a manipulation of a magnetic iso-spin qubit. At the same time the relocation correlates with the anti-crossing behavior of the two lowest electronic states of the quantum dot molecule and generates unusual features of the magnetic susceptibility of the system. It follows from this theoretical study that in our non-magnetic system we can perform and monitor the magnetic qubit. The qubit can be dynamically driven by an external magnetic field and retraced from the magnetic susceptibility changes. A few single-qubit quantum gates can be performed.
Optical reflection from a monolayer of embedded nano-objects covered by a thick capping layer
(2008)
Wijers, C. M. J.
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Voskoboynikov, O.
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
In a hybrid discrete-continuum description the optical response of a capped monolayer of nano-objects has been determined. The monolayer emits a summation of partial plane waves obeying traditional reflection and transmission, enabling solution of the monolayer dipole strength. For thick capping layers the resulting reflection coefficients could be approximated by analytical expressions. These results have been used to investigate the feasibility of experimental detection of the optical response of nano-object monolayers.
Optical response of layers of embedded semiconductor quantum dots
(2006-07-01)
Wijers, C. M. J.
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Chu, Jiun-Haw
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Liu, J. L.
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Voskoboynikov, O.
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電子工程學系及電子研究所
The influence of the surrounding semiconducting matrix upon the polarizability of embedded nanoobjects (quantum dots) has been investigated. The previously proposed hybrid model has been extended to accommodate the influence of embedding. It turns out that excess discrete dipoles having an excess polarizability against a uniform background identical to the dielectric host material build the basis for a modified discrete dipole model, suited to describe the optical response of this system. The individual dipoles are described by means of dielectric embedded oblate ellipsoids as to their static response. An efficient description of the electrostatics of these ellipsoids has been given in terms of explicit functions using cylindrical coordinates and compatible with similar derivations for spherical dielectric objects. The dynamic contribution, responsible for frequency dependence is determined quantum mechanically and added to the embedded bare polarizability. The result of the model for the particular InAs quantum dot GaAs host combination investigated is a slightly decreased internal reflectance as compared to vacuum and an overall strong increment of the absorbance, the structure in the reflectance and of the ellipsometric angles.
Optics of embedded semiconductor nano-objects using a hybrid model: bare versus dressed polarizabilities
(2006-11-01)
Wijers, C. M. J.
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Chu, J. -H.
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Voskoboynikov, O.
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The influence of the surrounding semiconducting matrix upon the optical response of embedded nano-objects (quantum dots) has been investigated. This system can be described by means of a hybrid model, where the full response is a combination of a macroscopic electrostatic response term and a dynamic response term, obtained quantum mechanically. The result is a modified discrete dipole model, where excess discrete dipoles having an excess polarizability with respect to a uniform background identical to the dielectric host material represent the response. In this model all electrodynamic interactions are screened by the host material. The electrostatic response is obtained by approximating the quantum dots by embedded dielectric oblate ellipsoids. Closed expressions for the electrostatic response of these ellipsoids have been derived. The electrodynamic nature of the dynamic quantum mechanical polarizability term however is unclear. It is not certain whether this polarizability is dressed or bare. Therefore we have investigated in detail the consequences of both options. Although there is no real qualitative difference between them, the difference is so large that experiment can easily discriminate between both. Results should be easily measurable anyhow.