Titanium/Silver Transition-Edge Sensors for Photon-Number-Resolving Measurement

In order to improve the performance of photon-number-resolving (PNR) superconducting transition-edge sensor (TES) devices, it is advantageous to use device materials with excellent thermal properties. We present TES devices based on a titanium/silver (Ti/Ag) bilayer structure which is expected to enable high-performance devices due to the high thermal conductivity and low specific heat of silver. We describe the fabrication process for our Ti/Ag devices and report their characterization results. We use the fabricated devices with a critical temperature of about 190 mK for PNR experiments at 1550 nm and shorter wavelengths, and demonstrate a high energy resolution of 0.17 eV and fast thermal recovery time of about 700 ns at the bias point of the best energy resolution. Judicious characterization of the device performance under various working conditions verifies its reliability and robustness, and proves that the Ti/Ag TES can support high-performance PNR measurement in demanding quantum optics experiments.