Kinetic-Inductance Detector Prototype to Distinguish Signal from Two-Level Defect Noise

Quantum defects within materials, identified as Two-Level Systems (TLSs), cause noise in astronomy kinetic inductance detectors (KIDs) and quantum information processors. Recognizing that TLSs will generally cause phase noise in KIDs, we develop a device which can potentially allow one to distinguish the intended photon signal from TLS noise. Here we report on a theory and experimental study of such a device. The device consists of two superconducting resonators sharing an electrical capacitance bridge that allows possible distinction between signal and noise. In the fabricated device, TLSs are within a deposited amorphous film that is the dielectric of the capacitors. One resonator mode uses TiN as an inductor and allows tuning of one bare resonator frequency into degeneracy with the other. Once tuned in this way, the resonator modes hybridize and the resonator field is zero in 2 of the 4 capacitors for each of the two hybridized modes. We find that with this so-called zero detuning, the individual resonator modes shift in an uncorrelated way from single-TLS noise, since each hybridized mode samples different TLSs . In contrast, the intended signal to one inductor of the KID induces known correlated changes to both modes such that they can be distinguished from TLS noise.