title: Non-Markovian suppression of charge qubit decoherence in the quantum point contact measurement.
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.
authors.affiliation: Physics Division, National Center for Theoretical Sciences, Tainan 70101, Taiwan, Republic of China. mtslee@gate.sinica.edu.tw
authors.forename: Ming-Tsung
authors.initials: MT
authors.lastname: Lee
authors.forename: Wei-Min
authors.initials: WM
authors.lastname: Zhang