Gap-Plasmon-Enhanced NbN Superconducting Photon Detectors at Single-Photon Level

Single-photon detectors have been widely studied for decades because of their unique capability to resolve photon numbers, enabling many applications in quantum information technologies. Compared to other types of single-photon detectors, niobium nitride (NbN) superconducting nanowire single-photon detectors are promising candidates and are commercially available today. However, the absorption coefficient of superconducting NbN in the visible range is typically low, resulting in low quantum efficiency and low signal-to-noise ratios. In the present work, we use a novel approach to enhance the visible-light photoresponse in NbN superconducting microwire photon detectors (SMPDs) by integrating them with gap plasmon resonators (GPRs). This talk describes how we observe the plasmonic NbN SMPDs can achieve a 233-fold enhancement in the phonon-electron interaction factor (γ) compared to pristine NbN SMPDs under resonant conditions with illumination at 532 nm. The nonlinear photoresponse in the visible region is attributed to the gap-plasmon-induced heating that breaks the superconducting state to normal. In addition, an impressive detection efficiency of 98% was achieved using these plasmonic SMPDs. Our results open new opportunities for designing sensitive quantum detectors for quantum information processing, quantum optics, imaging, and sensing at visible wavelengths. The detailed mechanisms and possible applications will be discussed.