Quantum measurement of a solid-state qubit by a mesoscopic detector is offundamental interest in quantum physics and an essential issue in quantumcomputing. In this work, by employing a unified quantum master equationapproach constructed in our recent publications, we study themeasurement-induced relaxation and dephasing of the coupled-quantum-dot statesmeasured by a quantum-point-contact. Our treatment pays particular attention onthe detailed-balance relation, which is a consequence of properly accountingfor the energy exchange between the qubit and detector during the measurementprocess. As a result, our theory is applicable to measurement at arbitraryvoltage and temperature. Both numerical and analytical results for the qubitrelaxation and dephasing are carried out, and new features are highlighted inconcern with their possible relevance to future experiments.
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