Rapid state purification protocols for a Cooper pair box

Abstract

We propose techniques for implementing two different rapid state purification schemes, within the constraints present in a superconducting charge qubit system. Both schemes use a continuous measurement of charge (z) measurements, and seek to minimize the time required to purify the conditional state. Our methods are designed to make the purification process relatively insensitive to rotations about the x-axis, due to the Josephson tunnelling Hamiltonian. The first proposed method, based on the scheme of Jacobs [Phys. Rev. A 67, 030301(R) (2003)] uses the measurement results to control bias (z) pulses so as to rotate the Bloch vector onto the x-axis of the Bloch sphere. The second proposed method, based on the scheme of Wiseman and Ralph [New J. Phys. 8, 90 (2006)] uses a simple feedback protocol which tightly rotates the Bloch vector about an axis almost parallel with the measurement axis. We compare the performance of these and other techniques by a number of different measures.

14 pages, 14 figures. v2: Revised version after referee comments. Accepted for publication by Physical Review B

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Cited by in corpus (11)

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• Efficient Quantum Filtering for Quantum Feedback Control
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• Rapid Measurement of Quantum Systems using Feedback Control
• Cyclic solid-state quantum battery: Thermodynamic characterization and quantum hardware simulation
• Rapid purification of quantum systems by measuring in a feedback-controlled unbiased basis
• Synthesis of maximally entangled mixed states and disentanglement in coupled Josephson charge qubits
• Optimality of qubit purification protocols in the presence of imperfections
• Quantum filtering one bit at a time
• Rapid-purification protocols for optical homodyning
• Optimal measurement-based feedback control for a single qubit: a candidate protocol