Proof of concept of the quantum capacitance detector

We fabricated and tested a proof-of-concept quantum capacitance detector, a superconducting radiation detector described in a recent publication [Shaw et al., Phys. Rev. B 79, 144511 (2009)]. In this concept, quasiparticle tunneling in a single Cooper-pair box is used to measure the density of quasiparticles in a superconducting absorber. We measured and characterized the response of the device to electrical quasiparticle injection obtaining its sensitivity. Moreover, we have converted the sensitivity to electrical noise-equivalent power, which is in the 10(-18) W/Hz(1/2) range at loading powers between 10(-15)-10(-16) W. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3339163]