arXiv subjects

Ming-Tsung Lee

Publications and source records attributed to Ming-Tsung Lee.

4 recordsLinked to original sources

arXiv2009

Exact Master Equation and Non-Markovian Decoherence for Quantum Dot Quantum Computing

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.

cond-mat.mes-hall↗

arXiv2008

Non-equilibrium theory of charge qubit decoherence in the quantum point contact measurement

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.

cond-mat.mes-hall↗

arXiv2006

Decoherence induced by electron accumulation in quantum measurement of charge qubits

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.

cond-mat.mes-hall↗

arXiv1997

Influence of Dynamical Pauli Effect and Dynamical Symmetry Breaking to Quantum Chaos

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.

chao-dyn↗