Aluminum–Titanium Bilayer for Near-Infrared Transition Edge Sensors

Transition-edge sensors (TESs) are single photon detectors attractive for applications in quantum optics and quantum information experiments owing to their photon number resolving capability. Nowadays, high-energy resolution TESs for telecommunication are based on either W or Au/Ti films, demonstrating slow recovery time constants. We report our progress on the development of an Al/Ti TES. Since bulk aluminum has a critical temperature (T(c)) of ca. 1.2 K and a sufficiently low specific heat (less than 10(−4) J/cm(3)K(2)), it can be employed to produce the sensitive material for optical TESs. Furthermore, exploiting its high T(c), Al-based TESs can be trimmed in a wider temperature range with respect to Ti or W. A first Al/Ti TES with a T(c) ≈ 142 mK, investigated from a thermal and optical point of view, has shown a response time constant of about 2 μs and single photon discrimination with 0.34 eV energy resolution at telecom wavelength, demonstrating that Al/Ti films are suitable to produce TESs for visible and NIR photon counting.