Optimality of qubit purification protocols in the presence of imperfections

Abstract

Quantum control is an essential tool for the operation of quantum technologies such as quantum computers, simulators, and sensors. Although there are sophisticated theoretical tools for developing quantum control protocols, formulating optimal protocols while incorporating experimental conditions remains a challenge. In this paper, motivated by recent advances in realization of real-time feedback control in circuit quantum electrodynamics systems, we study the effect of experimental imperfections on the optimality of qubit purification protocols. Specifically, we find that the optimal control solutions in the presence of detector inefficiency and non-negligible decoherence can be significantly different from the known solutions to idealized dynamical models. In addition, we present a simplified form of the verification theorem to examine the global optimality of a control protocol.

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• High-efficiency measurement of an artificial atom embedded in a parametric amplifier
• Completely Positive Quantum Trajectories with Applications to Quantum State Smoothing
• Observing quantum chaos with noisy measurements and highly mixed states
• Optimality of feedback control for qubit purification under inefficient measurement
• Global versus local optimality in feedback-controlled qubit purification: new insights from minimizing Rényi entropies
• Quantum feedback for measurement and control