title: Resonant cooper-pair tunneling: quantum noise and measurement characteristics.
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.
authors.affiliation: Department of Applied Physics and Physics, Yale University, New Haven, Connecticut, 06511, USA.
authors.forename: A A
authors.initials: AA
authors.lastname: Clerk
authors.forename: S M
authors.initials: SM
authors.lastname: Girvin
authors.forename: A K
authors.initials: AK
authors.lastname: Nguyen
authors.forename: A D
authors.initials: AD
authors.lastname: Stone