The sub-gap KID (SKID): on-chip spectroscopy at centimetric wavelengths
Résumé
We have fabricated planar indium oxide superconducting resonators (Tc around 3 K) that are sensitive to frequency-
selective radiation in the range 7?10 GHz. Those values lay more than 20 times below the equivalent superconducting
gap that is worth about 200 GHz. We show that the detected frequency can be adjusted by modulating the total
length of the superconducting resonator. The measured spectral resolution is of the order of thousands. We attribute
those observations to the excitation of higher-order resonance modes. The coupling between the fundamental (lumped)
and the higher order (distributed) resonances is related to the kinetic inductance non-linearity. These devices, that
we have called Sub-gap Kinetic Inductance Detectors (SKID), are to be distinguished from the standard kinetic
inductance detectors in which quasi-particles are generated when incident light breaks down Cooper pairs. We present
our preliminary results in the band 7-10 GHz and the plans for developing an instrument to monitor the water vapour
line at 22GHz.