Microwave engineering in superconducting nanowires for single-photon detection

Abstract

Detecting light at the single-photon level plays a crucial role in photonic quantum information processing, deep-space optical communication, astronomical observation, and biological and chemical sensing. With their exceptional performance, superconducting nanowire single-photon detectors (SNSPDs) have emerged as the leading single-photon counting technology at infrared wavelengths. Conventionally, the superconducting nanowires are treated as lumped circuit elements, and their microwave properties were largely neglected. In this thesis, we engineer the nanowires into kinetic-inductive transmission lines and use them to devise new single-photon detector architectures. Through impedance engineering, we developed a superconducting tapered nanowire detector that has increased output voltage, reduced timing jitter, and most importantly, the ability to resolve photon numbers. Utilizing the slow propagation speed of electrical signals in the nanowire transmission lines, we developed a delay-line-multiplexed detector array. This two-terminal array can perform coincidence counting over a large number of spatial modes and can be scalably integrated on photonic waveguides.