TY - JOUR

T1 - Observation of quantum capacitance in the Cooper-Pair transistor

AU - Duty, T.

AU - Johansson, G.

AU - Bladh, K.

AU - Gunnarsson, D.

AU - Wilson, C.

AU - Delsing, P.

PY - 2005/11/11

Y1 - 2005/11/11

N2 - We have fabricated a Cooper-pair transistor (CPT) with parameters such that for appropriate voltage biases, it behaves essentially like a single Cooper-pair box (SCB). The effective capacitance of a SCB can be defined as the derivative of the induced charge with respect to gate voltage and has two parts, the geometric capacitance, Cgeom, and the quantum capacitance CQ. The latter is due to the level anticrossing caused by the Josephson coupling and is dual to the Josephson inductance. It depends parametrically on the gate voltage and its magnitude may be substantially larger than Cgeom. We have detected CQ in our CPT, by measuring the in phase and quadrature rf signal reflected from a resonant circuit in which the CPT is embedded. CQ can be used as the basis of a charge qubit readout by placing a Cooper-pair box in such a resonant circuit.

AB - We have fabricated a Cooper-pair transistor (CPT) with parameters such that for appropriate voltage biases, it behaves essentially like a single Cooper-pair box (SCB). The effective capacitance of a SCB can be defined as the derivative of the induced charge with respect to gate voltage and has two parts, the geometric capacitance, Cgeom, and the quantum capacitance CQ. The latter is due to the level anticrossing caused by the Josephson coupling and is dual to the Josephson inductance. It depends parametrically on the gate voltage and its magnitude may be substantially larger than Cgeom. We have detected CQ in our CPT, by measuring the in phase and quadrature rf signal reflected from a resonant circuit in which the CPT is embedded. CQ can be used as the basis of a charge qubit readout by placing a Cooper-pair box in such a resonant circuit.

UR - http://www.scopus.com/inward/record.url?scp=18844382241&partnerID=8YFLogxK

U2 - 10.1103/PhysRevLett.95.206807

DO - 10.1103/PhysRevLett.95.206807

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AN - SCOPUS:18844382241

SN - 0031-9007

VL - 95

JO - Physical Review Letters

JF - Physical Review Letters

IS - 20

M1 - 206807

ER -