Detection of single infrared photons in superconducting microstrips of 4 nm thick disordered Nb0.15Re0.85 has been investigated. Microstrips with a critical temperature of 5.15 K and widths from 1.0 to 2.5  μm have been fabricated by optical lithography. We demonstrate single photon detection sensitivity at 1.5  μm wavelength at a temperature of 1.79 K. By investigating the detection process at this temperature, we find that the current bias threshold is at 21% of the depairing current. This threshold is similar to what should be observed in typical amorphous superconductors, which confirms that ultrathin disordered Nb0.15Re0.85 is an interesting material for superconducting microstrip single photon detectors that operate above 1 K.

Superconducting Microstrips Single Photon Detectors (SMSPDs) are currently of crucial interest in numerous applications thanks to their excellent performance in terms of high detection efficiency, short jitter time, and low dark count rate, meeting the necessities of covering a large active area using low-cost technology. In this scenario, the research of new materials to detect from telecom (1550 nm) to mid-infrared wavelengths plays an important role. In this work we fabricated SMSPDs made of NbRe, an innovative material recently proposed in this field. We realized devices with different microstrip configurations based on single microstrips and pairs of parallel microstrips to investigate the role of the geometry. Single photon detection sensitivity at 1550 nm wavelength at a temperature of 1.79 K was demonstrated. The results obtained are encouraging for the photon detection with NbRe-based devices covering large areas.

A photon number resolving detector (PNRD) is a device providing a different output depending on the number of incident photons in the single or few photons regime. This tool is crucial in several applications such as quantum communication, boson sampling, photon sources characterization and so on. PNRD are not new players in ultraviolet or visible wavelengths, but superconducting nanostrips provide a performing counterpart also in the near-infrared, where the aforementioned applications would like to operate. In this work we present a comprehensive description of the operation of an eight-pixel PNRD at the telecom wavelength of 1550 nm.

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