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Resonant Cooper-Pair Tunneling: Quantum Noise and Measurement Characteristics

A. A. Clerk, S. M. Girvin, A. K. Nguyen, A. D. Stone

DOI 10.1103/PhysRevLett.89.176804 · Physical Review Letters

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Abstract

We study the quantum charge noise and measurement properties of the double Cooper-pair resonance point in a superconducting single-electron transistor (SSET) coupled to a Josephson charge qubit. Using a density-matrix approach for the coupled system, we obtain a full description of the measurement backaction; for weak coupling, this is used to extract the quantum charge noise. Unlike the case of a nonsuperconducting SET, the backaction here can induce population inversion in the qubit. We find that the Cooper-pair resonance process allows for a much better measurement than a similar nonsuperconducting SET, and can approach the quantum limit of efficiency.

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