This work presents a comprehensive investigation of the influence of geometry-dependent factors on performance metrics of superconducting single-photon detectors. With fundamental knowledge, main investigations are focused to extend the spectral bandwidth and to enhance the detection efficiency, especially in infrared range. The developed technology of single-spiral detectors and unconventional electron-beam lithography allows to improve the performance of superconducting detectors.

This work presents a comprehensive investigation of the influence of geometry-dependent factors on performance metrics of superconducting single-photon detectors. With fundamental knowledge, main investigations are focused to extend the spectral bandwidth and to enhance the detection efficiency, especially in infrared range. The developed technology of single-spiral detectors and unconventional electron-beam lithography allows to improve the performance of superconducting detectors. This work was published by Saint Philip Street Press pursuant to a Creative Commons license permitting commercial use. All rights not granted by the work's license are retained by the author or authors.

Superconducting nanowire singe-photon detectors (SNSPD) are promising detectors in the field of applications, where single-photon resolution is required like in quantum optics, spectroscopy or astronomy. These cryogenic detectors gain from a broad spectrum in the optical and infrared range and deliver low dark count rates and low jitter times. This thesis improves the understanding of the detection mechanism of SNSPDs and intodruces new and promising multi-pixel readout concepts.

This work presents three advances to scale SNSPDs from few-pixel devices to large detector arrays: atomic layer deposition for the fabrication of uniform superconducting niobium nitride films of few-nanometer thickness, a frequency-multiplexing scheme to operate multiple detectors with a reduced number of lines, and the integration of SNSPDs with free-form polymer structures to achieve efficient optical coupling onto the active area of the detectors.

Superconducting nanowire singe-photon detectors (SNSPD) are promising detectors in the field of applications, where single-photon resolution is required like in quantum optics, spectroscopy or astronomy. These cryogenic detectors gain from a broad spectrum in the optical and infrared range and deliver low dark count rates and low jitter times. This thesis improves the understanding of the detection mechanism of SNSPDs and intodruces new and promising multi-pixel readout concepts. This work was published by Saint Philip Street Press pursuant to a Creative Commons license permitting commercial use. All rights not granted by the work's license are retained by the author or authors.

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.

This work investigates the capability of the high-temperature superconductor YBCO to sense the evolution of the electrical field of THz pulses. A deposition process for ten unit-cell thin films and a sub-μm patterning process were developed to enable high sensitivities. The detector response to THz exctiations and its electrical-field sensitivity were studied. This unique characteristic allows for the investigation of instabilities of the THz radiation emitted from synchrotron storage rings.

High-temperature superconductors have distinct advantages compared to conventional conductors. Below their critical temperature, superconductors have immeasurably low ohmic losses. To maintain the superconducting state, superconductors require constant cooling. This study aims at identifying the environmental impacts of the application of superconductors in future grid technologies such as superconducting power cables.