Analysis of quantum superconducting kinetic inductance photodetectors

Analysis of a quantum superconducting kinetic inductance photodetector (QSKIP) structure is presented for operation in a low background environment. We project the QSKIP's spectral response to be limited by the Cooper pair binding energy, 2 Delta or about 32 mu m for YBCO. The QSKIP response and sensitivity are computed from the minimum of the Hamiltonian energy functional and linearized Rothwarf-Taylor equations. Photoresponse and sensitivity expressions are computed in terms of the quasiparticle lifetime and indicate background limited infrared performance at very low photon flux levels. At low temperatures and under background limited infrared performance conditions, the photoresponse is proportional to the number of absorbed photons. Operating the QSKIP in the Meissner state and below 50% of the critical current limits the noise sources to fluctuations in the condensate population. With the noise and photoresponse equations, the QSKIP noise equivalent power is computed in terms of the characteristic lifetimes of: quasiparticle generation; quasiparticle recombination; anharmonic phonon decay; and phonon trapping. The calculated noise equivalent power for a YBCO QSKIP is about 2.5X10(-15) W/root Hz at 9 K. (C) 1995 American Institute of Physics.