Phonon-Trapping-Enhanced Energy Resolution in Superconducting Single-Photon Detectors

A pixel that can count individual photons and resolve each photon's color has been a dream for astronomers and biophysicists. Dream no longer! The authors realize such detectors using superconducting microwave resonators. The team experimentally shows that spectral resolving power is strongly limited by photon energy escaping through phonon losses to the bath, early in the detection process. With this insight, they use a thin membrane to demonstrate resolving power improved by a factor of 2.5, paving the way to reaching the fundamental limit in the future.