Efficient superconducting-nanowire single-photon detectors and their applications in quantum optics

Abstract

Superconducting-nanowire single-photon detectors (SNSPDs) are an emerging technology for infrared photon counting and detection. Their advantages include good device efficiency, fast operating speed, low dark-count rate, low timing jitter, free running mode, and no afterpulsing. The challenges to be addressed prior to real applications are cryogenic operations, small active areas, and efficiency-speed tradeoffs. This thesis presents the effort to address these challenges. A fiber-coupled SNSPD system with a large-area detector in a closed-cycle cryocooler has been built, demonstrating 24% system detection efficiency with a darkcount rate of -1000 counts/sec. As a result, the SNSPD system becomes a convenient tool with a single-mode fiber as the input channel and an SMA cable as the output channel. This system has enabled high-quality polarization-entanglement distribution at the wavelength of 1.3 tm. The 99.2% visibility in Hong-Ou-Mandel (HOM) interference measured in this experiment is the highest HOM visibility that has ever been reported for waveguide-based photon-pair sources. After entanglement is distributed, a pair rate of 5.8 pairs/sec at a pump power of 25 iW and two-photon quantum interference visibility of 97.7% have been measured. On the other hand, increasing the active area of the detector does decrease its speed. To address the issue of efficiency-speed tradeoff, SNSPDs have been integrated with optical nano-antennae. A 9- im-by-9- tm detector with 47% device efficiency and 5-ns reset time has been demonstrated. In terms of active area, device efficiency and speed, this SNSPD has the record performance among single-element SNSPDs. Finally, waveguide-integrated SNSPDs have been proposed and designed. The device structure permits efficient coupling of photons into a short nanowire, and thus, efficient and fast SNSPDs. This structure is compatible with on-chip photonic technologies, including inverse-taper couplers and ring resonators, that have been developed in recent years.