A TES single-photon detector demonstrating high-energy-resolution, high efficiency, and ultra-low dark counts near 0.9 <i>T</i> <i>c</i>

Transition-edge sensors (TESs) are among the most promising technologies for single-photon detection, offering high quantum efficiency, low dark count rates, and energy-resolving capabilities. However, optimal TES performance typically requires ultra-low temperatures below 100 mK, necessitating bulky dilution refrigerators or adiabatic demagnetization refrigerators, which limits their practical deployment. In this work, we demonstrate a titanium-based TES optimized for 1064 nm photon detection that achieves high performance at an elevated bath temperature of 220 mK—approximately 90% of its superconducting transition temperature, making it compatible with more compact sorption refrigerators. Through the integration of an optical cavity, a detailed complex impedance and noise characterization, and a systematic investigation of dark count sources, the detector achieves a system detection efficiency exceeding 97%, an energy resolution of 240 meV, and an intrinsic dark count rate as low as 2 × 10−4 cps. These findings significantly expand the applicability of TES single-photon detectors to practical photon-counting systems, such as quantum information and infrared astronomy.