Superconducting coplanar-waveguide (CPW) resonators made of NbTiN and Al have shown photon noise limited detection for optical loading equivalent to the typical sky signal at modern sub-mm telescopes. While the detection efficiency of these hybrid MKIDs is equal to the value expected based on antenna simulation and the known efficiency of quasiparticle generation, this is not the case for conventional CPW MKIDs made from pure Al. Given that the hybrid MKIDs use the large gap superconductor NbTiN to trap photo-excited quasiparticles in the sensitive area of the resonator made from Al, it is postulated that the origin of the lower detection efficiency of pure Al resonators is due to quasiparticle diffusion. During the conference we will report on the measurements comparing NbTiN/Al and pure Al resonators and the effect of quasiparticle diffusion on the detection efficiency of these MKIDs.
In this paper, we present a novel design of a compact, double-fold half-wave superconducting coplanar waveguide resonator, specifically optimized for quantum readout. The geometry offers advantages in terms of scalability and allows for a more compact integration of qubits per unit area. The superconducting resonators are designed to operate within a fundamental frequency range of 1.9 GHz$-
1.95GHz,utilizingbothgapandfingercouplingschemes.Thedevicesarefabricatedusingthinaluminumfilmsdepositedonhigh−resistivitysapphiresubstrates.Theproposedresonatorsexhibitqualityfactor(Q_{L}
)of2.9× 10^{5}$and 1.58 ×
103for gap coupled and finger coupled, respectively, during experimental measurements. The simulated Q
Lof single-folded meander line resonators are found to be 4.65 ×
105and 258.42, for gap coupled and finger coupled, respectively, for comparison purpose at similar operating frequency. A comprehensive analysis of the microwave transmission spectra was conducted at cryogenic temperatures near 10 mK, across very high input drive powers ($-
30dBmto-
10dBm).Experimentalresultsshowagoodagreementwithsimulationsandtheequivalentlumpedcircuitmodel.Notably,theproposeddesignreducesthephysicalfootprintoftheresonatordevicesupto28.2\%
comparedtoconventionalsingle−foldmeanderedstructures.TheresonatorsdemonstratestrongpotentialforintegratingqubitswithreadoutandcontrolbusesinquantuminformationprocessingwhichrequireaQ_{L}$between
104−105. They also being well-suited for cryogenic detector applications that utilize microwave kinetic inductance detector (MKID) arrays in frequency multiplexing for different coupling schemes.