Experimental demonstration of a resolving power of 25-55 at 1545-402 nm wavelengths with photon-counting MKIDs

A noiseless, photon counting detector is desired for low light applications in astronomy. We study superconducting Microwave Kinetic Inductance Detectors (MKIDs) in which the intrinsic energy resolution eliminates the conventional dark current. A visible/near-IR photon creates thousands of quasiparticles through electron-phonon interaction. Phonons lost in this process limit the energy resolution to E/dE<20 (10) for aluminium MKIDs on solid substrate, measured with a 402 (1545) nm laser. When fabricated on a 120 nm SiN membrane, E/dE increases to 55 (25), which demonstrates that phonons are more effectively trapped, and that the promises on resolving power for MKIDs are realistic.