Resonant cooper-pair tunneling: quantum noise and measurement characteristics

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 b...

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Bibliographic Details
Published in:Physical review letters 2002-10, Vol.89 (17), p.176804-176804, Article 176804
Main Authors: Clerk, A A, Girvin, S M, Nguyen, A K, Stone, A D
Format: Article
Language:English
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Summary: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.
ISSN:0031-9007
1079-7114
DOI:10.1103/PhysRevLett.89.176804