Cryogenic Dielectric Metasurface-Integrated Superconducting Nanowire Single-Photon Detectors

Over the past decade, multielement superconducting nanowire single-photon detectors (SNSPDs) have emerged as the leading single-photon detection technology due to their exceptional system detection efficiency (SDE), ultrahigh timing precision, and negligible dark counts. However, achieving these performances with a single-element SNSPD has been an outstanding challenge due to a fundamental trade-off: A large active area is necessary for high SDE, whereas a smaller area is crucial for higher photon count rates, lower dark counts, and lower jitter. Here, we introduce a dielectric cryogenic metalens integrated with a single-element SNSPD to achieve high SDE with a smaller active area. We report a $\sim$ 77-fold enhancement in the SDE of a metalensed SNSPD with a 5 $\mu$ m $\times$ 5 $\mu$ m active area, compared with an identical reference SNSPD without a metalens, using a moderately sized 60 $\mu$ m $\times$ 60 $\mu$ m metalens. Next, we theoretically demonstrate polarization-resolved photodetection at the telecommunication wavelength using a bifunctional metalens. We achieve a cross-detection probability of $<$ 2 $\%$ between metalensed SNSPDs spaced at 10 $\mu$ m under illumination with x- and y-polarized light. Integrating a multifunctional cryogenic metasurface with the state-of-the-art SNSPDs may enable novel capabilities with reduced size, weight, power, cost, and cooling (SWaP- $C^2$ ) requirements.