High‐Efficiency Photon‐Number‐Resolving Detectors based on Hafnium Transition‐Edge Sensors

Generation of nonclassical states of light is at the foundation of numerous quantum optics experiments and optical quantum information processing implementations. One such non‐Gaussian optical quantum state can be obtained by photon subtraction from a squeezed optical state. Photon‐number‐resolving detectors with high efficiency and low dark counts are needed for heralding the subtraction of one, two or more photons. Transition‐edge sensors (TES) optimized for high detection efficiency at 850 nm, seem to be ideal heralding detectors for such quantum optics experiments. In this work, we describe the fabrication and characterization of hafnium TESs embedded in an optical structure for optimal absorption at 850 nm. Accurate measurements of optical constants for all materials and fine control of layer thicknesses in the optical cavity should increase the detector efficiency to values higher than 95%.