Browsing by Author "Chen, YN"

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Alignment and orientation of absorbed dipole molecules
(2004-12-01)
Liao, YY
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Chen, YN
;
Chuu, DS
;
電子物理學系
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Department of Electrophysics
Half-cycle laser pulse is applied on an absorbed molecule to investigate its alignment and orientation behavior. Crossover from field-free to hindered rotation motion is observed by varying the angel of hindrance of potential well. At small hindered angle, both alignment and orientation show sinusoidal-like behavior because of the suppression of higher excited states. However, mean orientation decreases monotonically as the hindered angle is increased, while mean alignment displays a minimum point at certain hindered angle. The reason is attributed to the symmetry of wave function and can be explained well by analyzing the coefficients of eigenstates.
An optional operation organization of Chiang Kai-Shek International Airport rail link project in Taiwan
(2005)
Hsu, YC
;
Chou, YH
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Chen, YN
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運輸與物流管理系註：原交通所+運管所
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Department of Transportation and Logistics Management
With CKS International Airport remains one the important gateways to Taiwan, the CKS International Airport rail link system would serve as a most crucial mass transportation tool that would poise to excel the competitiveness of the international airport and its adjacent metropolises. In light of which, how best to locate an optimal operating organization that offers a sustainable management would emerge as a pressing concern. Taking into account urban transit and airport rail link service, the study, upon analyzing using the FAHP and TOPSIS methods, has chosen the Taipei Mass Rapid Transit Corporate alternative as the optimized alternative, together with the alternative of setting up a new private-run company as the second best alternative. As derived from analyses conducting on various decision-making groups, an operator with actual transportation operations would emerge as a crucial determining factor to become the future airport rail link operator. The study findings are not only intended as references to government departments but also to recommend the government to expeditiously finalize the operator as an urgent mission to facilitate subsequent implementation in light of the complexity in the rail system's interfacing logistical implementation.
Bound state of the quantum dot formed at intersection of L- or T-shaped quantum wire in inhomogeneous magnetic field
(2002-03-01)
Lin, YK
;
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
A quantum dot (QD) can be formed at the intersection of the symmetric or asymmetric L-shaped (LQW) or T-shaped quantum wire (TQW). The bound state energies in such QD systems surrounded by inhomogeneous magnetic fields are found to depend strongly on the asymmetric parameter alpha=W-2/W-1, i.e., the ratio of the arm widths and magnetic field applied on the wire arms. Two effects of the magnetic field on the bound state energy of the electron can be obtained. One is the depletion effect which purges the electron out of the QD system. The other is to create an effective potential due to the quantized Landau levels of the magnetic field. Depletion effect is found to be more prominent in weak field region. Our results show the bound state energy of the electron in such QD system depends quadratically (linearly) on the magnetic field in the weak (strong) field region. It is also found that the bound state energy of the electron depends on the magnetic field strength only and not on its direction. A simple model is proposed to explain the behavior of the magnetic dependence of the bound state energy of the electron both in weak and strong magnetic field regions. The contour plots of the relative probability of the bound state in LQW or TQW in magnetic field are also presented. (C) 2002 American Institute of Physics.
Bound states of L- or T-shaped quantum wires in inhomogeneous magnetic fields
(2001-11-15)
Lin, YK
;
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The bound-state energies of L- or T-shaped quantum wires in inhomogeous magnetic fields are found to depend strongly on the asymmetric parameter alpha = W-2/W-1, i.e, the ratio of the arm widths. Two effects of magnetic field on bound-state energies of the electron are obtained. One is the depletion effect, which purges the electron out of the OQD system. The other is to create an effective potential due to quantized Landau levels of the magnetic field. The bound-state energies of the electron in L- or T-shaped quantum wires are found to depend quadratically (linearly) on the magnetic field in the weak- (strong-) field region and are independent of the direction of the magnetic field. A simple model is proposed to explain the behavior of the magnetic dependence of the bound-state energy in both weak- and strong-magnetic field regions.
Current detection of superradiance and induced entanglement of double quantum dot excitons
(2003-04-25)
Chen, YN
;
Chuu, DS
;
Brandes, T
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電子物理學系
;
Department of Electrophysics
We propose to measure the superradiance effect by observing the current through a semiconductor double-dot system. An electron and a hole are injected separately into one of the quantum dots to form an exciton and then recombine radiatively. We find that the stationary current shows oscillatory behavior as one varies the interdot distance. The amplitude of oscillation can be increased by incorporating the system into a microcavity. Furthermore, the current is suppressed if the dot distance is small compared to the wavelength of the emitted photon. This photon trapping phenomenon generates the entangled state and may be used to control the emission of single photons at predetermined times.
Decay rate and renormalized frequency shift of a quantum wire Wannier exciton in a planar microcavity
(2001-09-15)
Chen, YN
;
Chuu, DS
;
Brandes, T
;
Kramer, B
;
電子物理學系
Super-radiant decay rate and frequency shift of a Wannier exciton in a one-dimensional quantum wire are studied. It is shown that the dark-mode exciton can be examined experimentally when the quantum wire is embedded in a planar microcavity. It is also found that the decay rate is greatly enhanced as the cavity length L-c is equal to the multiple wavelength of the emitted photon. Similar to its decay-rate counterpart, the frequency shift also shows discontinuities at resonant modes.
Decay rate and renormalized frequency shift of superradiant exciton in a cylindrical quantum wire
(2003-06-01)
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The decay rate and renormalized frequency shift of superradiant exciton in a cylindrical quantum wire are studied. The transition behavior from 1D wire to 2D film is examined through the property of the radiative decay. Similar to the case in a quantum well, the decay rate of the higher mode exciton is larger than that of the lower mode one. Moreover, it is also found the decay rate and frequency shift do not show oscillatory dependence on wire radius because of the conservation of angular momentum. (C) 2003 Elsevier Science B.V. All rights reserved.
Decay rate and renormalized frequency shift of superradiant excitons: Crossover from two-dimensional to three-dimensional crystals
(2000-04-15)
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The superradiant decay rate and renormalized frequency shift of Wannier excitons in a semiconductor film of N layers are studied. It is found that both the decay rate and renormalized frequency shift show oscillatory dependence on layer thickness. The crossover from the superradiant exciton to the bulk polariton when varying N from 1 to infinity is also examined.
Decay rate of a Wannier exciton in low-dimensional systems
(2001-05-01)
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The superradiant decay rate of a Wannier exciton in a one-dimensional system is studied. The crossover behavior from 1D chain to 2D film is also examined. It is found that the decay rate shows a oscillatory dependence on the channel width L. When the quasi-1D channel is embeded with planar microcavities, it is show that the dark mode exciton can be examined experimentally.
Effect of electron-phonon interaction on the impurity binding energy in a quantum wire
(2000-09-01)
Chuu, DS
;
Chen, YN
;
Lin, YK
;
電子物理學系
;
Department of Electrophysics
The effect of electron-optical phonon interaction on the hydrogenic impurity binding energy in a cylindrical quantum wire is studied. By using Landau and Pekar variational method, the Hamiltonian is separated into two parts which contain phonon variable and electron variable, respectively. A perturbative-variational technique is then employed to construct the trial wave function for the electron part. The effect of confined electron-optical phonon interaction on the binding energies of the ground state and an excited state are calculated as a function of wire radius. Both the electron-bulk optical phonon and electron-surface optical phonon coupling are considered. It is found that the energy corrections of the polaron effects on the impurity binding energies increase rapidly as the wire radius is shrunk, and the bulk-type optical phonon plays the dominant role for the polaron effects. (C) 2000 Elsevier Science B.V. All rights reserved.
Orientation of adsorbed dipolar molecules: A conical well model
(2006-03-01)
Liao, YY
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Chen, YN
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Chou, WC
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Chuu, DS
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電子物理學系
Orientation of single and two coupled polar molecules irradiated by a single laser pulse under a conical-well model is investigated theoretically. The orientation of a single hindered rotor shows a periodic behavior. In particular, the amplitude of the oscillation is sensitive to the degree of alternation of the laser field. Crossover from field-free to hindered rotation is observed by varying the hindering angle for different heights of conical wells. For a small hindering potential and angle, time-averaged orientation differs greatly from that for an infinite one. The orientation at a large hindering angle shows irregularlike behavior under strong dipole-dipole interaction. Entanglement induced by the dipole-dipole interaction is also calculated for the coupled-rotor system, in which the time-averaged entropy increases monotonically as the hindering angle is increased. The competition between the confinement effect and dipole interaction is found to dominate the behavior of the coupled-rotor system.
Orientations of two coupled molecules
(2004-11-11)
Liao, YY
;
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
Orientation states of two coupled polar molecules controlled by laser pulses are studied theoretically. By varying the period of a series of periodically applied laser pulse, transition from regular to chaotic behavior may occur. Schmidt decomposition is used to measure the degree of entanglement. It is found that the entanglement can be enhanced by increasing the strength of laser pulse. (C) 2004 Elsevier B.V. All rights reserved.
Proposal for teleportation of charge qubits via super-radiance
(2005-08-18)
Chen, YN
;
Li, CM
;
Chuu, DS
;
Brandes, T
;
電子物理學系
A scheme is proposed to teleport charge qubits via super-radiance. Reservoir-induced entanglement is generated between two semiconductor dots in a microcavity where a quantum state encoded in a third quantum dot is then tuned into collective decay with one of the entangled dots. Teleportation is achieved automatically in our scheme which we also extend to quantum wires.
Renormalized frequency shift of a Wannier exciton in a one-dimensional system
(2004-04-05)
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The radiative frequency shift of superradiant exciton in a one-dimensional system is calculated. It is shown that a finite frequency shift can be obtained after proper renormalization. The value of the shift is inversely proportional to the factor lambda/d, where lambda is the wavelength of the emitted photon and d is the lattice spacing. (C) 2004 Elsevier B.V. All rights reserved.
Resonant tunneling into a quantum dot embedded inside a microcavity
(2002-10-15)
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
We propose to measure the Purcell effect by observing the current through a semeiconductor quantum dot embedded in a microcavity. An electron and a hole are injected separately into the quantum structure to form an exciton and then recombine radiatively. The stationary current is shown to be altered if one varies the cavity length or the exciton energy gap. Therefore, the Purcell effect can be observed experimentally by measuring the current through the quantum structure. In addition, we also find that super-radiance of excitons between quantum dots may also be observed in an electrical way.
Rotational entangled states between two coupled molecules
(2006-01-28)
Liao, YY
;
Chen, YN
;
Li, CM
;
Chuu, DS
;
電子物理學系
A method is proposed to create entanglement between two coupled identical polar molecules separated at a distance of tens of nanometres. Entangled states of two coupled polar molecules controlled by half-cycle pulses are studied theoretically. The von Neumann entropy is calculated to characterize the degree of entanglement. By varying the pulse shape of the applied laser, transition from regular to irregular behaviour occurs. Moreover, the entanglement is also found to be enhanced by applying multiple laser pulses. The behaviour from quantum to classical limit is also discussed.
Shot noise of quantum ring excitons in a planar microcavity
(2005-12-01)
Chen, YN
;
Chuu, DS
;
Cheng, SJ
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電子物理學系
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Department of Electrophysics
Shot noise of quantum ring (QR) excitons in a p-i-n junction surrounded by a microcavity is investigated theoretically. Some radiative decay properties of a QR exciton in a microcavity can be obtained from the observation of the current noise, which also gives extra information about one of the tunnel barriers. A different noise feature between the quantum dot (QD) and QR is pointed out, and may be observed in a suitably designed experiment.
Shot-noise spectrum of superradiant entangled excitons
(2004-06-01)
Chen, YN
;
Brandes, T
;
Li, CM
;
Chuu, DS
;
電子物理學系
The shot noise produced by tunneling of electrons and holes into a double dot system incorporated inside a p-i-n junction is investigated theoretically. The enhancement of the shot noise is shown to originate from the entangled electron-hole pair created by superradiance. The analogy to the superconducting Cooper pair box is pointed out. A series of Zeno-like measurements is shown to destroy the entanglement, except for the case of maximum entanglement.
Spin relaxation in a GaAs quantum dot embedded inside a suspended phonon cavity
(2006-02-01)
Liao, YY
;
Chen, YN
;
Chuu, DS
;
Brandes, T
;
電子物理學系
The phonon-induced spin relaxation in a two-dimensional quantum dot embedded inside a semiconductor slab is investigated theoretically. An enhanced relaxation rate is found due to the phonon van Hove singularities. Oppositely, a vanishing deformation potential may also result in a suppression of the spin relaxation rate. For larger quantum dots, the interplay between the spin orbit interaction and Zeeman levels causes the suppression of the relaxation at several points. Furthermore, a crossover from confined to bulklike systems is obtained by varying the width of the slab.
Superradiant and Aharonov-Bohm effect for the quantum ring exciton
(2004-05-01)
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The Aharonov-Bohm and superradiant effect on the radiative decay rate of an exciton in a quantum ring is studied. With the increasing of ring radius, the exciton decay rate is enhanced by superradiance, while the amplitude of AB oscillation is decreased. The competition between these two effects is shown explicitly and may be observable in time-resolved experiments. (C) 2004 Elsevier Ltd. All rights reserved.