Superconducting nanowire single photon detectors (SNSPDs) are a highly promising emerging photon counting technology, offering infrared sensitivity combined with low dark count rates and sub-100 ps timing jitter [1]. These devices are under consideration for a wide variety of photon counting applications, from quantum cryptography to remote sensing. Next generation device designs based on optical cavities, ultra narrow wires, parallel wire arrays and nano-antenna enhanced devices are being evaluated to meet the demands of advanced photon counting applications.
Superconducting nanowire single photon detectors (SNSPDs) are a highly promising emerging photon counting technology, offering infrared sensitivity combined with low dark count rates and sub-100 ps timing jitter [1]. These devices are under consideration for a wide variety of photon counting applications, from quantum cryptography to remote sensing. Next generation device designs based on optical cavities, ultra narrow wires, parallel wire arrays and nano-antenna enhanced devices are being evaluated to meet the demands of advanced photon counting applications.
Single-photon detectors based on superconducting nanowires (SSPDs or SNSPDs) have rapidly emerged as a highly promising photon-counting technology for infrared wavelengths. These devices offer high efficiency, low dark counts and excellent timing resolution. In this review, we consider the basic SNSPD operating principle and models of device behaviour. We give an overview of the evolution of SNSPD device design and the improvements in performance which have been achieved. We also evaluate device limitations and noise mechanisms. We survey practical refrigeration technologies and optical coupling schemes for SNSPDs. Finally we summarize promising application areas, ranging from quantum cryptography to remote sensing. Our goal is to capture a detailed snapshot of an emerging superconducting detector technology on the threshold of maturity.
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.
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.
We present an overview of recent results for new generation of infrared and optical superconducting nanowire single-photon detectors (SNSPDs) that has already demonstrated a performance that makes them devices-of-choice for many applications. 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, SNSPDs are also compatible with an integrated optical platform as a crucial requirement for applications in emerging quantum photonic technologies. By embedding SNSPDs in nanophotonic circuits we realize waveguide integrated single photon detectors which unite all desirable detector properties in a single device.
Superconducting Nanowire Single Photon Detectors (SNSPDs) excel at a wide variety of performance criteria for single photon counting. They combine unprecedented high detection efficiency, high timing resolution, high count rates, low intrinsic dark count rates, and are sensitive to ultraviolet through mid-infrared single-photons. At JPL, we are working on several projects to push the performance limits of SNSPDs to achieve higher maximum count rates, larger active areas, higher timing resolution, and a wider spectral range. Our recent advances enable new applications for dark matter detection, imaging, and space-to-ground communication and provide insight into the fundamental physics of single-photon detection in superconducting nanowires.
Superconducting nanowire single photon detectors (SNSPDs) are a rapidly maturing detector technology that offer superior performance relative to competing infrared photon counting technologies. The original experimental work presented here explores three novel methods of improving and analysing detector characteristics, employing low-temperature piezoelectric motors at temperatures below 4 K in a closed-cycle cryostat. Utilizing the low-temperature piezoelectric nanopositioners in tandem with a miniature confocal microscope, this work specifically shows a spatially-separable parallel-wire SNSPD demonstrating one- and two-pixel photon discrimination, with the detector responding more quickly when triggering two pixels. The work demonstrates nanoantenna-coupled SNSPDs, which are simulated, designed, and tested using the same nano-optical setup. In these an increased local absorption into the nanowire is seen at the antennas' resonant wavelengths, enhancing the efficiency of the detector by up to 130 %. Finally, a modified optical setup using a distributed Bragg reflector fibre in place of the microscope to form a tunable cavity around two configurations of SNSPD is demonstrated, improving absorption of the incident light into the nanowire across the whole active area. For these, enhancement in the system detection efficiency of up to 40 % is seen.