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.
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.
Single photon detection advanced rapidly in the last decade. The superconducting nanowire single-photon detector (SNSPD) is an emerging technology, which offers low dark count rates, broadband sensitivity from visible to mid-infrared wavelengths and very high quantum efficiency. All these features are appealing for future emerging applications in remote gas sensing, quantum key distribution and quantum information processing. By enclosing the detector in an optical cavity, tuned to the operating wavelength, the total system detection of the SNSPD is improved. Based on the cavity design, the detector absorption is boosted at the desired experimental wavelength. Devices have been fabricated and tested, in this thesis, with enhanced detection efficiency at near-infrared, infrared and mid-infrared wavelengths. NbTiN detectors fabricated on Ta2O5 / SiO2 distributed Bragg reflectors (DBR) for front-side coupling exhibit a system detection efficiency of ≈ 90% at λ = 940 nm for the best device measured. SNSPDs were also fabricated in NbTiN on metallic mirrors for back-side coupling for 1550 and 2333 nm experimental wavelengths. The first design exhibited a system detection efficiency of ≈ 84.5%, at λ = 1550 nm for the best device measured. The second exhibited low system detection efficiency since the device suffered from unexpectedly high dark count rate mainly due to blackbody radiation at 2.2 K. However, it was possible to measure the timing jitter of this device at 350 mK indicating a FWHM of 84 ps. Another technique to improve the total system detection efficiency of the SNSPD, is by fabricating a hairpin-shaped nanowire atop a single mode waveguide. In this design, photons travel through the waveguide and via evanescent coupling are absorbed in the nanowire. These SNSPD devices have been designed to thread along single mode Si ridge waveguides using a hairpin-shaped nanowire structure, which offers enhanced coupling and absorption efficiency via evanescent coupling. These ultra-thin superconducting MoSi detectors are precisely patterned on top of a single mode Si waveguide (600 nm) with alignment error less than 40 nm. Low temperature electrical and nano-optical characterization was carried out using a two-stage pulse tube (PT) coldhead, using an additional 4He / 3He sorption pump, low vibration characterization of SNSPD devices at 350 mK was carried out. Characterised devices exhibit low dark count rate <5 counts per second and timing jitter of ≈ 83 ps full width half maximum (FWHM) at wavelength (λ) = 1550 nm and at critical current ≈ 30 µA.
Fast and efficient detection of single photons with high timing accuracy is a crucial requirement in most quantum optics experiments and enables novel sensing and imaging solutions. Superconducting nanowire single-photon detectors (SNSPD) achieve technology-leading performance in terms of detection efficiency, dark count rate, timing jitter, and detector dead times. However, conventional SNSPDs with high system detection efficiency typically rely on resonant enhancement of the absorption efficiency, thus only achieving attractive detector benchmarks over narrow spectral windows. Waveguide-integrated SNSPDs allow for leveraging the wideband material absorption in superconducting nanowires by absorbing light in a traveling-wave geometry but have been limited to low system detection efficiencies due to interface losses when coupling to optical fibers. Here, we show how high system detection efficiencies of 22%–73% are realized over a broad wavelength range from 532 nm to 1640 nm in a single waveguide-integrated SNSPD device. We accomplish efficient coupling between optical fibers and waveguide-integrated nanowire detectors by employing a 3D interface, produced in direct laser writing, that relies on total internal reflection for achieving a broad transmission bandwidth. We further find low timing jitter of 25.7 ps and detector decay times of 9.8 ns, allowing for single-photon counting with high repetition rates up to 100 MHz. Our work paves the way for an efficient single-photon detector solution that combines the spectral requirements of an extremely wide range of quantum optics experiments in a single device. The coupling approach and SNSPD-integration with nanophotonic circuits are further well-suited for realizing large-scale detector arrays.
Superconducting nanowire single-photon detectors (SNSPDs) provide high efficiency for detecting individual photons while keeping dark counts and timing jitter minimal. Besides superior detection performance over a broad optical bandwidth, compatibility with an integrated optical platform is a crucial requirement for applications in emerging quantum photonic technologies. Here we present SNSPDs embedded in nanophotonic integrated circuits which achieve internal quantum efficiencies close to unity at 1550 nm wavelength. This allows for the SNSPDs to be operated at bias currents far below the critical current where unwanted dark count events reach milli-Hz levels while on-chip detection efficiencies above 70% are maintained. The measured dark count rates correspond to noise-equivalent powers in the 10(-19) W/Hz(-1/2) range and the timing jitter is as low as 35 ps. Our detectors are fully scalable and interface directly with waveguide-based optical platforms.
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.
Near infrared photons are a promising choice for quantum information processing; their low transmission loss is necessary for applications such as long distance Quantum Key Distribution (QKD) in optical fibre and integrated quantum optics. An ideal proof-of-concept test of such applications would be to create, manipulate and detect single photons on a monolithic chip. Superconducting nanowire single photon detectors promise high system detection efficiencies, low dark count and low jitter under near-infrared photon illumination. Superconducting nanowire devices using NbTiN films show improved coupling efficiencies with the aid of oxidized silicon cavities. NbTiN devices were characterised in a fibre-coupled package, achieving high SDE (43%) coherent key generation rates over 200km in a T12 QKD protocol simulation. Hairpin superconducting nanowires offer excellent integration with silicon waveguide optics and can achieve near unity absorption efficiencies. Hairpin devices fabricated from MoSi films were characterised using a custom pulse tube He-3 cryostat engineered for low vibration operation at 350mK and capable of near-infrared optical maps of superconducting nanowires. The devices exhibited high critical currents 40uA), low jitter (51ps) and a dark count rate <10cps. Tests of perpendicular coupling efficiencies yield low system detection efficiencies due to high coupling losses. Using an alternative coupling method via grating couplers or cleave mounting, it is expected a much higher system detection efficiency can be achieved.
In the field of quantum technologies, the superconducting nanowire single photon detector(SNSPD) is nowadays well recognized as a key enabling device. SNSPDs combine high detectionefficiency in the visible and near IR spectral ranges, timing jitter as low as 10 ps, low dark count rate(<100 s−1) and cut-off frequency above 100 MHz. These features make it particularly attractive e.g. forfundamental quantum optics experiments and quantum communications.Plug-and-play SNSPDs with fibered optical access, as shown in Figure 1, are based on a meandernanowire defined by patterning an ultrathin (<10 nm) superconducting film. The device is designedso that absorption of a single photon is enough to brake locally the superconducting order, and toinduce a measurable change of the wire’s resistance. Until recently, such devices displayed two mainlimitations: (1) their efficiency did not exceed ~40% due to the limited optical absorption of the thinfilm; and (2) their response was strongly polarization-sensitive, due to the optical anisotropy of thenanowire. I will present two different approaches which enable to get very high (>90% [1]) andpolarization-insensitive [2,3] detection efficiency. We consider designs based on the integration of thenanowire within an optical microcavity (compatible with the plug-and-play configuration) or on topof an optical waveguide (preferred approach for integration in photonic circuits). I will finally discussnovel application prospects of such detectors, with emphasis on photon-number resolution.