Superconducting single-photon detectors (SSPDs) have developed into a mature device technology and excel due outstanding performance metrics, in particular high detection efficiency combined with high time resolution and low dark count rate for a wide wavelength range from the visible to the mid-infrared. In addition to commercially available systems with devices coupled to optical fibers, SSPDs can be integrated with photonic circuits using scalable nanofabrication technologies. Here, we will present recent progress on SSPDs based on NbTiN thin films and their integration on different photonic material platforms. Our process for NbTiN growth at room temperature will be described, using magnetron reactive co-sputtering to achieve high-quality superconducting layers down to thicknesses of few nanometres. Optimized SSPD devices are realized by tuning the superconducting properties of NbTiN thin films, adjusting the material composition and nanocrystalline structure. The realization of different types of detectors and geometries will be shown, including nanofabrication techniques for achieving fully suspended nanowire structures. Furthermore, we will discuss challenges and prospects for scaling-up SSPD device technology as well as detector systems. Multiplexing schemes such as dispersion engineering of superconducting transmission lines will be highlighted as powerful approach to address multiple detectors and reduce the number of required feedthroughs and electrical lines in the cryostat. Eventually, exemplary applications of SSPDs for photon counting in quantum optics and light detection and ranging (LIDAR) will be outlined.
Superconducting single-photon detectors (SSPDs) have developed into a mature device technology and excel due outstanding performance metrics, in particular high detection efficiency combined with high time resolution and low dark count rate for a wide wavelength range from the visible to the mid-infrared. In addition to commercially available systems with devices coupled to optical fibers, SSPDs can be integrated with photonic circuits using scalable nanofabrication technologies. Here, we will present recent progress on SSPDs based on NbTiN thin films and their integration on different photonic material platforms. Our process for NbTiN growth at room temperature will be described, using magnetron reactive co-sputtering to achieve high-quality superconducting layers down to thicknesses of few nanometres. Optimized SSPD devices are realized by tuning the superconducting properties of NbTiN thin films, adjusting the material composition and nanocrystalline structure. The realization of different types of detectors and geometries will be shown, including nanofabrication techniques for achieving fully suspended nanowire structures. Furthermore, we will discuss challenges and prospects for scaling-up SSPD device technology as well as detector systems. Multiplexing schemes such as dispersion engineering of superconducting transmission lines will be highlighted as powerful approach to address multiple detectors and reduce the number of required feedthroughs and electrical lines in the cryostat. Eventually, exemplary applications of SSPDs for photon counting in quantum optics and light detection and ranging (LIDAR) will be outlined.
Superconducting nanowire single-photon detectors (SNSPDs) are renowned for their high detection efficiency, low dark count rate, and fast timing resolution, which have emerged as an essential device in quantum technologies, including quantum computing and communication, which also significantly benefits classical applications such as deep-space communication, neuromorphic computing, and light detection and ranging (LiDAR). However, designing and customizing SNSPD into versatile functionalities to satisfy these intensive requirements poses significant challenges, including thin-film deposition, nanofabrication, electrical integration, and light delivery strategies. While prior work has typically optimized individual steps – such as fabrication or characterization – there is a lack of reported systematic, integrated frameworks that span all stages from device design to performance benchmarking. This gap hinders broader adoption of the technology across scientific and industrial communities and limits the rigorous exploration of advanced detection concepts. This thesis aims to establish an end-to-end workflow for the customizable fabrication and comprehensive characterization of superconducting nanowire single-photon detectors, and to demonstrate that such a platform is essential for the investigation of diverse single-photon detection architectures. It begins with the optimization of NbTiN thin-film deposition utilizing an ultrahigh vacuum sputtering system. By systematically identifying and optimizing key deposition parameters, we achieve NbTiN films with targeted superconducting properties along with high uniformity and reproducibility. This fast and reliable workflow establishes a solid foundation for detector fabrication and provides instructions for flexible control over film properties. Furthermore, effective nanofabrication protocols for the high-quality SNSPDs were elaborated, along with the specialized cryogenic packaging techniques for reliable electrical and optical integration. The achieved devices demonstrated performance metrics comparable to commercial systems. The implementation of this full fabrication—characterization cycle also enabled flexible exploration of advanced detector architectures. For example, we investigated superconducting microbridge single-photon detectors (SMSPDs) as a complementary platform, demonstrating a fivefold enhancement in signal-to-noise ratio and a tenfold reduction in recovery time relative to conventional SNSPDs. These results provide quantitative insight into detector design trade-offs. Within this framework, photon-number-resolving (PNR) detection using SNSPDs was further investigated as an essential function for advanced quantum and classical applications. We presented innovative detector architectures—interleaved multi-pixel arrays and multilayer coherent absorption structures—to overcome limitations inherent in conventional multiplexing methods, such as nonuniform detection, temporal degradation, and crosstalk. An interleaved multi-pixel SNSPD array with up to four-photon resolution was achieved with uniform detection, as well as a multilayer architecture based on coherent absorption with uniform and near-unity absorption efficiency. Importantly, a theoretical comparison between these two architectures was conducted to evaluate their absorption efficiency and PNR performance, offering insights into structural optimization and device scalability for advanced PNR detectors. Overall, this thesis establishes a fully in-house SNSPD fabrication and characterization capability, providing a robust foundation for the development, customization, and evaluation of high-performance superconducting single-photon detectors. This platform enables reproducible design optimization, quantitative performance benchmarking, and systematic exploration of detector architectures. By integrating fabrication, characterization, and architectural innovation within a consistent workflow, it facilitates both fundamental investigation and application-driven advancement of single-photon detection technologies in our laboratory and the broader research community in Singapore.
Single photon detectors are a vital part of many emerging technologies which harness the quantum properties of light to benefit the fields of communication, computation and sensing. Superconducting nanowire single photon detectors (SNSPDs) offer high detection efficiency, low dark count rates, low timing jitter, and infrared sensitivity that are required by the most demanding single photon counting applications. This thesis presents SNSPDs fabricated and tested at the University of Glasgow that are integrated with optical structures which enable enhanced detection efficiency and integration with waveguide circuit technology. The monolithic integration of waveguide circuit components presents a route towards realisation of an optical quantum information processor that has the stability and scalability to perform the demanding tasks of quantum computation. A novel process is introduced for incorporating superconducting detectors with single mode gallium arsenide waveguides and quantum dot single photon sources. Together these elements would enable the generation of quantum states of light which could be manipulated and detected on a single chip. Detectors are patterned in NbTiN thin superconducting films on to suspended nanobeam waveguides with better than 50 nm alignment accuracy. Low temperature electrical and optical testing confirms the detectors’ single photon sensitivity under direct illumination as well as to waveguide coupled light. Measured detectors were found to have internal registering efficiencies of 6.8 ± 2.4%. Enhancing absorption of photons into thin superconducting films is vital to the creation of high efficiency superconducting single photon detectors. Fabricating an SNSPD on a dielectric mirror creates a partial cavity that can be tailored to enhance detection of light at specific wavelengths. Devices have been fabricated and tested in this thesis with enhanced detection efficiency at infrared and visible wavelengths for quantum cryptography, remote sensing and life science applications. Detectors fabricated in NbTiN on GaAs/AlGaAs Bragg mirrors exhibited a system detection efficiency of 1.5% at 1500 nm wavelength for the best device measured. SNSPDs were also fabricated in NbN on aperiodic dielectric mirrors with a range of different bandwidths. A peak system detection efficiency of 82.7% at 808 nm wavelength was recorded.
Abstract The advancement of superconducting nanowire single-photon detectors (SNSPDs or SSPDs) is intrinsically linked to breakthroughs in superconducting materials engineering. These detectors are prized for their excellent sensitivity and performance across a wide wavelength range, from ultra-violet to mid-infrared (mid-IR). Plasma-enhanced atomic layer deposition (ALD) is an advanced deposition technique that enables exceptional film uniformity across large wafers, making it ideal for a variety of applications. In this study, ALD NbTiN films are fabricated into SNSPDs that exhibit single-photon response across near- to mid-IR wavelengths. A 5 nm thick NbTiN film was patterned into devices consisting of ∼100 nm wide meandered nanowires, and the nanowire cross-section and composition were analysed by transmission electron microscopy. The devices were tested in a closed-cycle cryostat with a base temperature of 0.9 K. Photon detection rate and timing jitter were measured across the wavelength range 1.5–4.4 µ m under low dark count conditions, confirming single-photon sensitivity across the measured wavelength bands. This work introduces the ALD-grown NbTiN films as a new platform for SNSPD detectors, achieving mid-IR single-photon sensitivity. The intact film quality after fabrication demonstrates the potential of ALD processes for scalable infrared detector technologies.
Superconducting nanowire single photon detectors (SNSPD) offer excellent performance for infrared single photon detection, combining high efficiency, low timing jitter, low dark count rates and high photon counting rates. Promising application areas for SNSPDs include quantum key distribution, space-to-ground communications and single photon remote sensing [1]. SNSPDs are typically made with ultrathin niobium nitride (NbN) films with thickness 4 nm and a superconducting transition temperature above 9 K. NbN offers high performance in the near infrared but their sensitivity drops at wavelengths beyond 2 um. There is growing interest in potential photon counting applications in the mid infrared domain (for example remote sensing of greenhouse gases in the atmosphere [2]). One way to overcome the wavelength limit in NbN SNSPDs is to use films with a lower superconducting energy gap [3]. Here we report on the study of SNSPDs fabricated with thin films of titanium nitride (TiN). We compare TiN films deposited by atomic layer deposition (ALD) and by magnetron sputtering. The TiN films range in thickness from 5 to 60 nm, with superconducting transition temperatures from ~1 K to 3.5 K. We have analyzed the films via transmission electron microscopy and variable angle spectroscopic ellipsometry. We characterize TiN SNSPDs performance from near to mid-infrared at wavelengths (1-4 um) with fast optical parametric oscillator (OPO) source. We compare the performance of TiN SNSPDs to devices based on other lower gap materials: MoSi, NbTiN, WSi. [1] Natarajan et al Superconductor Science and Technology 25 063001 (2012) [2] Abshire et al Laser Applications to Chemical, Security and Environmental Analysis, (Optical Society of America, 2008) paper LMA4 [3] Verma et al Applied Physics Letters 105 022602 (2014)
In this review, we present recent advances relating to superconducting nanowire single-photon detectors (SSPDs or SNSPDs) and their broad range of applications. During a period exceeding ten years, the system performance of SSPDs has been drastically improved, and lately excellent detection efficiencies have been realized in practical systems for a wide range of target photon wavelengths. Owing to their advantages such as high system detection efficiency, low dark count rate, and excellent timing jitter, SSPDs have found application in various research fields such as quantum information, quantum optics, optical communication, and also in the life sciences. We summarize the photon detection principle and the current performance status of practical SSPD systems. In addition, we introduce application examples in which SSPDs have been applied.
Integration of superconducting devices on photonic platforms opens up a wide range of functionalities and applications. We report on NbTiN thin films deposited on SiO2, Si3N4, GaAs, LiNbO3, and AlN as well as on a monolayer of hexagonal boron nitride, using a universal reactive co-sputtering recipe. The morphology and the superconducting properties of the NbTiN thin films with a thickness of 10 nm were characterized by atomic force microscopy and electrical transport measurements. Superconducting strip photon detectors were fabricated using a design suitable for waveguide integration and compared in terms of their internal quantum efficiency and detection pulse kinetics. Our results show well-comparable performances for detectors integrated on different platforms, while also demonstrating that reactive co-sputter deposition of NbTiN at room temperature provides a robust method for realizing superconducting devices on various materials.