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Ph.D. Defense Tuesday, February 27, 2007 Bourns Hall – A275 10:00AM Title: Measurement and Feedback Control of Solid-State Qubits Abstract: In this dissertation we consider several problems related to design, measurement, and feedback control of solid-state qubits. First, we study a double-quantum-dot qubit with the Bayesian quantum feedback, designed to maintain perfect coherent oscillations for an arbitrarily long time. The effects of dephasing environment, detector nonideality, and qubit parameter deviations on the quantum feedback efficiency are analyzed analytically and using Monte Carlo simulations. We also take into account a finite signal bandwidth and a time delay in the feedback loop. Second, we present geometrical modeling of superconducting charge qubit designs in order to calculate the capacitance matrix. Third, we analyze measurement errors for superconducting phase qubits. Using analytical approaches as well as numerical solution of the time-dependent Schrödinger equation, we study several one-qubit error mechanisms, including nonadiabatic effects, incomplete state discrimination, and qubit repopulation. We also calculate two-qubit errors due to crosstalk in the process of measurement of capacitively coupled phase qubits, and find the limitations for the coupling capacitance. The results of the analysis are important for the design of future quantum gates based on phase qubits. |
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