title: Direct observation of Josephson capacitance.
abstract: The effective capacitance has been measured in the split Cooper-pair box (CPB) over its phase-gate bias plane. Our low-frequency reactive measurement scheme allows us to probe purely the capacitive susceptibility due to the CPB band structure. The data are quantitatively explained using parameters determined independently by spectroscopic means. In addition, we show in practice that the method offers an efficient way to do nondemolition readout of the CPB quantum state.
authors.affiliation: Low Temperature Laboratory, Helsinki University of Technology, FIN-02015 HUT, Finland.
authors.forename: M A
authors.initials: MA
authors.lastname: Sillanpää
authors.forename: T
authors.initials: T
authors.lastname: Lehtinen
authors.forename: A
authors.initials: A
authors.lastname: Paila
authors.forename: Yu
authors.initials: Y
authors.lastname: Makhlin
authors.forename: L
authors.initials: L
authors.lastname: Roschier
authors.forename: P J
authors.initials: PJ
authors.lastname: Hakonen