The viewpoint by Daniel Santavicca (2018 Supercond. Sci. Technol. 31, 040502) on “Prospects for faster, higher-temperature superconducting nanowire single-photon detectors”, calls for the attention on the letter by M Ejrnaes et al (2017 Supercond. Sci. Technol.30 12LT02 https://doi.org/10.1088/1361-6668/aa94b9).
Superconducting nanostrips are the sensitive elements of SNSPDs (Superconducting Nanostrip Single-Photon Detectors) that have demonstrated single-photon detection in the visible and near-infrared with near unity quantum efficiency, ∼ns reset times, very low dark count rates, and ∼10 ps timing resolution. As a result, SNSPDs have become attractive for some of the most demanding single-photon applications such as quantum cryptography, deep space communication, and single-molecule fluorescence. In this work, researchers at CNR-SPIN Napoli (Mikkel Ejrnaes, Roberto Cristiano), Università degli Studi di Napoli ‘Federico II’ (Loredana Parlato, Giampiero Pepe, Francesco Tafuri) and Chalmers University of Technology, Göteborg, Sweden (Riccardo Arpaia, Thilo Bauch, Floriana Lombardi), have observed dark pulses in 10nm thick, 65 nm wide and 80 nm long YBCO nanostrips. The nanostrips were fabricated at the Chalmers University of Technology and the measurements were carried out at CNR-SPIN laboratories in Pozzuoli, Napoli. Below 10 K, the current–voltage curves exhibit hysteretic behavior, a hallmark of the unstable electrothermal feedback necessary for proper SNSPD operation. In this temperature range, dark counts are observed in form of current pulses. The shape of these pulses appears very similar to the dark count pulses from conventional SNSPDs.
While challenges remain, says Santavicca, the work by Ejrnaes et al represents an important step toward the realization of single photon detectors made of superconductors with high critical temperature, Tc. SNSPD are typically made from low-Tc superconductors. High-Tc materials have also been explored, with limited success to date. A higher critical temperature offers two important advantages: a higher operating temperature, which makes the devices more attractive for many applications; and the possibility of a significantly faster count rate.