Mid-infrared photon counting with superconducting nanowires

Single-photon counting has become an essential tool in quantum optics experiments, as well as remote sensing and life science applications. However conventional technologies such as single-photon avalanche diodes, as well as the availability of standard telecom optical components, has limited much of this work to the near infrared/telecom wavelength range. Superconducting nanowire single photon detectors (SNSPDs) have emerged in recent years as the gold standard in photon counting applications due to their low dark count rates, fast timing resolution and high efficiency [1]. SNSPDs have also demonstrated photon counting efficiency out to much greater wavelengths which enables us to explore new experimental possibilities in the mid-infrared [2]. In this work we design and fabricate mid-infrared SNSPDs and deploy them in a variety of photon counting experiments [3,4]. The devices are based on a NbTiN superconducting film integrated into an optical cavity to enhance absorption in the mid-infrared. We characterise these devices using an optical parametric oscillator, tuneable between 1.5 m and 4.2 m. We then deploy these in a proof-of-principle tabletop light detection and ranging (LIDAR) experiment at 2.3 m. LIDAR in the mid-infrared is attractive due to spectral regions of low atmospheric absorption and reduced solar background photon flux, when compared to telecom wavelengths. We also present results from a photon-pair source operating at 2 m. This is a key resource for extending quantum optics and quantum secure communications to the mid infrared domain. Pairs are generated using a custom lithium niobate crystal and detected using SNSPDs. We demonstrate two-photon interference and polarisation entanglement of the photon pairs at 2 m. This work opens the pathway to future development of quantum optics and quantum technologies in the mid-infrared spectral region. References [1] Gol’tsman et al Applied Physics Letters 79 705 (2001) [2] Marisli et al Nano Letters 12 (9) 4799 (2012) [3] G. G. Taylor et al Optics Express 26 (27) 38147 (2018) [4] S. Prabhakar et al Science Advances 6 (13) eaay5195 (2019)