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ABSTRACT: In this article, we report the recent progress on decoherence dynamics of electrons in quantum dot quantum computing systems
using the exact master equation we derived recently based on the Feynman–Vernon influence functional approach. The exact master
equation is valid for general nanostructure systems coupled to multi-reservoirs with arbitrary spectral densities, temperatures
and biases. We take the double quantum dot charge qubit system as a specific example, and discuss in details the decoherence
dynamics of the charge qubit under coherence controls. The decoherence dynamics risen from the entanglement between the system
and the environment is mainly non-Markovian. We further discuss the decoherence of the double-dot charge qubit induced by
quantum point contact (QPC) measurement where the master equation is re-derived using the Keldysh non-equilibrium Green function
technique due to the non-linear coupling between the charge qubit and the QPC. The non-Markovian decoherence dynamics in the
measurement processes is extensively discussed as well.
Quantum Information Processing 04/2012; 8(6):631-646. · 2.00 Impact Factor
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ABSTRACT: The electrochemical behavior of anodically deposited manganese oxide was studied in pyrrolidinium formate (P-HCOO), 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6), and 1-ethyl-3-methylimidazolium thiocyanate (EMI-SCN) ionic liquids (ILs). The experimental data indicate that the Mn oxide electrode showed ideal pseudocapacitive performance in aprotic EMI-SCN IL. In a potential window of approximately 1.5 V, the oxide specific capacitance, evaluated using cyclic voltammetry and chronopotentiometry, was about 55 F/g. The electrochemical energy storage reaction was examined using X-ray photoelectron spectroscopy (XPS). It was confirmed that the SCN- anions, instead of the EMI+ cations, were the primary working species that can become incorporated into the oxide and thus compensate the Mn3+/Mn4+ valent state variation upon the charge-discharge process. According to the analytical results, a pseudocapacitive mechanism of Mn oxide in the SCN- based aprotic IL was proposed.
Langmuir 08/2009; 25(19):11955-60. · 4.19 Impact Factor
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ABSTRACT: Pseudocapacitive characteristics of manganese (Mn) oxide were recognized in aprotic ionic liquid (IL), namely, butylmethylpyrrolidinium−dicyanamide (BMP−DCA), within a potential window of 3 V. The electrochemical energy storage mechanism was examined using X-ray photoelectron spectroscopy and in situ X-ray absorption spectroscopy. It was confirmed that the DCA− anions, instead of the bigger BMP+ cations, were the working species that compensate the Mn valent state variation upon charging and discharging in the IL electrolyte. During oxidation of the Mn oxide electrode, to keep the charges balanced, the quasi-linear DCA− anions were inserted into the tunnels between the MnO6 octahedral units, expanding the structural framework. Importantly, a highly reversible process was observed during the subsequent reduction step. XPS depth profiling analyses showed that the electrochemical reaction thickness was approximately 50 nm.
06/2009;
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ABSTRACT: A nonequilibrium theory describing the charge qubit dynamics measured by a quantum point contact is developed based on Schwinger-Keldysh's approach. Using the real-time diagrammatic technique, we derive the master equation to all orders in perturbation expansions. The non-Markovian processes in the qubit dynamics is naturally taken into account. The qubit decoherence, in particular, the influence of the tunneling-electron fluctuation in the quantum point contact with a longer correlation time comparing to the time scale of the qubit dynamics, is studied in the framework. We consider the Lorentzian-type spectral density to characterize the channel mixture of the electron-tunneling processes induced by the measurement, and determine the correlation time scale of the tunneling-electron fluctuation. The result shows that as the quantum point contact is casted with a narrower profile of the spectral density, tunneling electrons propagate in a longer correlation time scale and lead to the non-Markovian processes of the qubit dynamics. The qubit electron in the charge qubit can be driven coherently. The quantum point contact measurement with the minimum deviation of the electron-tunneling processes prevents the qubit state from the decoherence.
The Journal of chemical physics 01/2009; 129(22):224106. · 3.09 Impact Factor
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ABSTRACT: Iron addition was attempted in this study to improve the pseudo-capacitive property of Mn oxides. The oxides were prepared
on graphite substrates by anodic deposition. The deposition solutions were
manganese acetate
aqueous solutions with various amount of
(up to
). Crystal structure and surface morphology of the deposited oxides were examined by X-ray diffraction and scanning electron
microscopy, while their chemical state was analyzed by X-ray photoelectron spectroscopy and X-ray absorption near edge structure.
Moreover, specific capacitances of the oxide electrodes were determined by cyclic voltammetry in
electrolyte. Experimental results indicated that the incorporated iron presented as divalent and trivalent forms in the binary
oxides. Although iron addition did not change the nanocrystalline structure of the deposited Mn oxide, it caused the chemical
state and surface morphology variations of the oxide electrodes. Consequently, their pseudo-capacitive performances were modified.
The optimum specific capacitance of
was found for the oxide deposited in the solution containing
. The value was 21% higher than that of the plain Mn oxide. Capacitance-retained ratio of the oxide after 1000 charge-discharge
cycles was also improved from 70 to 85% because of iron addition.
Journal of The Electrochemical Society. 08/2007; 154(9):A875-A881.
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ABSTRACT: A non-equilibrium theory describing the charge qubit dynamics measured by a quantum point contact is developed based on Schwinger-Keldysh's approach. Using the real-time diagram technique, we derive the master equation to all orders in perturbation expansions. The non-Markovian processes in the qubit dynamics is naturally taken into account. The qubit decoherence, in particular, the influence of the tunneling-electron fluctuation in the quantum point contact with a longer time correlation, is studied in the framework. We consider the Lorentzian-type spectral density to characterize the channel mixture of the electron tunneling processes induced by the measurement and determine the correlation time scale of the tunneling-electron fluctuation. The result shows that as the quantum point contact is casted with a narrower profile of the spectral density, tunneling electrons can propagate with a longer time correlation and lead to the non-Markovian processes of the qubit dynamics. The qubit electron in the charge qubit will be driven coherently. The quantum point contact measurement with the minimum deviation of the electron tunneling processes prevents the qubit state from the decoherence. Comment: 14 pages, 7 figures
08/2007;
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ABSTRACT: In this paper, we study the quantum decoherence induced by accumulation of electron tunnelings during the quantum measurement of a charge qubit. The charge qubit is a single electron confined in coupled quantum dots. The measurement of the qubit states is performed using a quantum point contact. A set of master equations for qubit states is derived within a nonequilibrium perturbation to the equilibrium reservoir due to the electron accumulation between the source and drain of the quantum point contact. The quantum decoherence of the qubit states arose from the electron accumulation during the measurement is explored in this framework, and several interesting results on charge qubit decoherence are obtained. Comment: 14 pages, 6 figures, To appear in Phys. Rev. B
11/2005;
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ABSTRACT: In this paper, we study the influence of quantum effects to chaotic dynamics, especially the influence of Pauli effect and dynamical symmetry breaking to chaotic motions. We apply the semiquantal theory to the Sp(6) fermion symmetry model in nuclear collective motion. We demonstrate that quantum chaos appears when dynamical symmetry is broken. We further show that dynamical Pauli effect enhances quantum chaos.
10/1997;
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ABSTRACT: Fibrous morphology and nano-crystalline nature of the anodically deposited manganese oxide were confirmed by a transmission electron microscope (TEM). The oxide electrode exhibited an ideal capacitive behavior as indicated by cyclic voltammetry (CV). In order to explore the energy storage mechanism, variation of electronic and structural aspects of the manganese oxide induced by changing the applied potential was studied in situ in aqueous 2 M KCl by Mn K-edge X-ray absorption spectroscopy (XAS). Position shift of the adsorption edge, toward higher energy during oxidation and backward lower energy during reduction, was clearly recognized. The experimental results directly proved for the first time that the pseudo-capacitance of the manganese oxide was attributed to its continuous and reversible faradic redox reaction during the charge–discharge process.
Journal of Power Sources.
