Abstract: We report the pulse-to-pulse timing jitter measurement of a niobium nitride (NbN) superconducting single-photon detector (SSPD) and an InGaAs avalanche photodiode (APD) at 1550-nm wavelength. A direct comparison of their timing jitter was performed by using the same experimental configuration to measure both detectors. The measured jitter of the SSPD and the APD are 75 and 84 ps at full-width at half-maximum (FWHM), and 138 and 384 ps at full-width at tenth-maximum (FWTM), respectively. The jitter of the SSPD remains small at FWTM while that of APD is wide. We also estimated the transmission distances and secure key generation rates for fiber-based quantum key distribution (QKD) which uses these detectors. The estimated transmission distances of the APD are 86 km and 107 km with respect to 1 ns and 100 ps time windows, respectively, and those of the SSPD are 125 km and 172 km with respect to 1 ns and 100 ps time windows, respectively. This estimation indicates the SSPDЃfs advantages for QKD compared to the APD.

Abstract: We present an active anti-latching system for superconducting nanowire single-photon detectors. We experimentally test it against a bright-light attack, previously used to compromise security of quantum key distribution. Although our system detects continuous blinding, the detector is shown to be partially blindable and controllable by specially tailored sequences of bright pulses. Improvements to the countermeasure are suggested.

Abstract: We report our studies on spectral sensitivity of meander-type, superconducting NbN thin-film single-photon detectors (SPDs), characterized by GHz counting rates of visible and near-infrared photons and negligible dark counts. Our SPDs exhibit experimentally determined quantum efficiencies ranging from ∼0.2% at the 1.55 μm wavelength to ∼70% at 0.4 μm. Spectral dependences of the detection efficiency (DE) at the 0.4 to 3.0-μm-wavelength range are presented. The exponential character of the DE dependence on wavelength, as well as its dependence versus bias current, is qualitatively explained in terms of superconducting fluctuations in our ultrathin, submicron-width superconducting stripes. The DE values of large-active-area NbN SPDs in the visible range are high enough for modern quantum communications.

Abstract: We have measured the quantum efficiencysQEd, GHz counting rate, jitter, and noise-equivalentpowersNEPdof nanostructured NbN superconducting single-photon detectorssSSPDsdin thevisible to infrared radiation range. Our 3.5-nm-thick and 100- to 200-nm-wide meander-typedevices(total area 10310mm2), operating at 4.2 K, exhibit an experimental QE of up to 20% inthe visible range and,10% at 1.3 to 1.55mm wavelength and are potentially sensitive up tomidinfrareds,10mmdradiation. The SSPD counting rate was measured to be above 2 GHz withjitter,18 ps, independent of the wavelength. The devices’ NEP varies from,10−17W/Hz1/2for1.55mm photons to,10−20W/Hz1/2for visible radiation. Lowering the SSPD operatingtemperature to 2.3 K significantly enhanced its performance, by increasing the QE to,20% andlowering the NEP level to,3310−22W/Hz1/2, both measured at 1.26mm wavelength.

Abstract: We have realized superconducting single photon detectors with reduced inductance and increased signal pulse amplitude. The detectors are based on a parallel connection of ultrathin NbN nanowires with a common bias inductance. When properly biased, an absorbed photon induces a cascade switch of all the parallel wires generating a signal pulse amplitude of 2mV. The parallel wire configuration lowers the detector inductance and reduces the response time well below 1ns.
This work was performed in the framework of the EU project “SINPHONIA” NMP4-CT-2005-016433.

Abstract: We analyze the ultimate performance of a superconducting quantum detector in order to meet requirements for applications in near-infrared astronomy and X-ray spectroscopy. The detector exploits a combined detection mechanism, in which avalanche quasiparticle multiplication and the supercurrent jointly produce a voltage response to a single absorbed photon via successive formation of a photon-induced and a current-induced normal hotspot in a narrow superconducting strip. The response time of the detector should increase with the photon energy providing energy resolution. Depending on the superconducting material and operation conditions, the cut-off wavelength for the single-photon detection regime varies from infrared waves to visible light. We simulated the performance of the background-limited infrared direct detector and X-ray photon counter utilizing the above mechanism. Low dark count rate and intrinsic low-frequency cut-off allow for realizing a background limited noise equivalent power of 10−20 W Hz−1/2 for a far-infrared direct detector exposed to 4-K background radiation. At low temperatures, the intrinsic response time of the counter is rather determined by diffusion of nonequilibrium electrons than by the rate of energy transfer to phonons. Therefore, thermal fluctuations do not hamper energy resolution of the X-ray photon counter that should be better than 10−3 for 6-keV photons. Comparison of new data obtained with a Nb based detector and previously reported results on NbN quantum detectors support our estimates of ultimate detector performance.

Abstract: An experimental demonstration of a subcarrier-wave quantum cryptography system with superconducting single-photon detectors (SSPDs) that distributes a secure key in a single-mode fiber at distance of 25 km with a bit rate of 800 kbit/s, a distance of 100 km with a bit rate of 19 kbit/s, and a distance of 200 km with a bit rate of 0.18 kbit/s is described.

Abstract: We investigate the response mechanism of nanowire superconducting single-photon detectors (SSPDs) made of amorphous MoxSi1-x. We study the dependence of photon count and dark count rates on bias current in magnetic fields up to 113 mT at 1.7 K temperature. The observed behavior of photon counts is similar to the one recently observed in NbN SSPDs. Our results show that the detecting mechanism of relatively high-energy photons does not involve the vortex penetration from the edges of the film, and on the contrary, the detecting mechanism of low-energy photons probably involves the vortex penetration from the film edges.

Abstract: Single-photon detectors1 at near-infrared wavelengths with high system detection efficiency (>90%), low dark count rate (<1 c.p.s.), low timing jitter (<100 ps) and short reset time (<100 ns) would enable landmark experiments in a variety of fields2, 3, 4, 5, 6. Although some of the existing approaches to single-photon detection fulfil one or two of the above specifications1, to date, no detector has met all of the specifications simultaneously. Here, we report on a fibre-coupled single-photon detection system that uses superconducting nanowire single-photon detectors7 and closely approaches the ideal performance of single-photon detectors. Our detector system has a system detection efficiency (including optical coupling losses) greater than 90% in the wavelength range λ = 1,520–1,610 nm, with a device dark count rate (measured with the device shielded from any background radiation) of ~1 c.p.s., timing jitter of ~150 ps full-width at half-maximum (FWHM) and reset time of 40 ns.

Abstract: The possibility of creating NbN superconducting single-photon detectors with saturated dependence of quantum efficiency (QE) versus normalized bias current was investigated. It was shown that the saturation increases for the detectors based on finer films with a lower value of Rs300/Rs20. The decreasing of Rs300/Rs20 was related to the increasing influence of quantum corrections to conductivity of superconductors and, in turn, to the decrease of the electron diffusion coefficient. The best samples have a constant value of system QE 94% at Ib/Ic ~ 0.8 and wavelength 1310 nm.

Abstract: Superconducting nanowire single-photon detectors (SNSPD) are used in quantum optics when record-breaking time resolution, high speed, and exceptionally low levels of dark counts (false readings) are required. Their detection efficiency is limited, however, by the absorption coefficient of the ultrathin superconducting film for the detected radiation. One possible way of increasing the detector absorption without limiting its broadband response is to make a detector in the form of several vertically stacked layers and connect them in parallel. For the first time we have studied single-photon detection in a multilayer structure consisting of three superconducting layers of amorphous tungsten silicide (WSi) separated by thin layers of amorphous silicon. Two operating modes of the detector are illustrated: an avalanche regime and an arm-trigger regime. A shift in these modes occurs at currents of ∼0.5–0.6 times the critical current of the detector.
This work was supported by technical task No. 88 for scientific research at the National Research University “Higher School of Economics,” Grant No. 14.V25.31.0007 from the Ministry of Education and Science of Russia, and the work of G. N. Goltsman was supported by task No. 3.7328.2017/VU of the Ministry of Education and Science of Russia.

Abstract: We present thorough measurements of the intrinsic detection efficiency in the wavelength range from 350 to 2500 nm for meander-type TaN and NbN superconducting nanowire single-photon detectors with different widths of the nanowire. The width varied from 70 nm to 130 nm. The open-beam configuration allowed us to accurately normalize measured spectra and to extract the intrinsic detection efficiency. For detectors from both materials the intrinsic detection efficiency at short wavelengths amounts at 100% and gradually decreases at wavelengths larger than the specific cut-off wavelengths, which decreases with the width of the nanowire. Furthermore, we show that applying weak magnetic fields perpendicular to the meander plane decreases the smallest detectable photon flux.

Abstract: Dynamics of a resistive hotspot formation by near-infrared-wavelength single photons in nanowire-type superconducting NbN stripes was investigated. Numerical simulations of ultrafast thermalization of photon-excited nonequilibrium quasiparticles, their multiplication and out-diffusion from a site of the photon absorption demonstrate that 1.55 μm wavelength photons create in an ultrathin, two-dimensional superconducting film a resistive hotspot with the diameter which depends on the photon energy, and the nanowire temperature and biasing conditions. Our hotspot model indicates that under the subcritical current bias of the 2D stripe, the electric field penetrates the superconductor at the hotspot boundary, leading to suppression of the stripe superconducting properties and accelerated development of a voltage transient across the stripe.

Abstract: We are investigating the possibility of using NbN nanowires as detectors in time-of-flight mass spectrometers for investigation of macromolecules of interest in biology (proteins). NbN nanowires could overcome the two major drawbacks encountered so far by cryogenic detectors, namely the low working temperature in the mK region and the slow temporal response. In fact, NbN nanowires can work at 5 K and the response time is at least a factor 10–100 better than that of other cryogenic detectors. We present a feasibility study based on a numerical code to calculate the response of a NbN nanowire. The parameter space is investigated at different energies from IR to macromolecules (i.e. from eV to keV) in order to understand if larger value of film thickness and width can be used for the keV energy region. We also present preliminary experimental results of irradiation with X-ray photons of NbN to simulate the effect of macromolecules of the same energy.

Abstract: We describe the design and characterization of a fiber-coupled double-channel single-photon detection system based on superconducting single-photon detectors (SSPD), and its application for quantum optics experiments on semiconductor nanostructures. When operated at 2-K temperature, the system shows 10% quantum efficiency at 1.3-¿m wavelength with dark count rate below 10 counts per second and timing resolution <100 ps. The short recovery time and absence of afterpulsing leads to counting frequencies as high as 40 MHz. Moreover, the low dark count rate allows operation in continuous mode (without gating). These characteristics are very attractive-as compared to InGaAs avalanche photodiodes-for quantum optics experiments at telecommunication wavelengths. We demonstrate the use of the system in time-correlated fluorescence spectroscopy of quantum wells and in the measurement of the intensity correlation function of light emitted by semiconductor quantum dots at 1300 nm.

Abstract: В работе представлены результаты разработки и создания чувствительных и ультрабыстрых приемников, основанных на тонкопленочных сверхпроводниковых наноструктурах: болометрах на эффекте электронного разогрева (HEB – hot-electron bolometer) и детекторах одиночных фотонов видимого и инфракрасного диапазонов волн (SSPD – superconducting singe-photon detector). Представлены основные принципы работы сверхпроводниковых устройств, технология создания и конструкционные особенности приемников, их основные типы и характеристики. Достигнутые рекордные значения параметров приемных систем позволяют использовать созданные приборы при решении различных научно-исследовательских задач в ближнем, среднем и дальнем ИК диапазонах волн.
This work presents the results of the development and fabrication of sensitive and ultrafast detectorsbased on thin film superconducting nanostructures: hot-electron bolometers (HEBs) and visible and infrared superconducting singe photon detectors (SSPDs). The main operational principles of the superconducting devices are presentedas well as the technology of fabrication of the detectors and their main types and parameters. The achieved record parameters of the detectors allow application of the fabricated devices to solution of various research problems in the near, middle and far IR ranges.

Abstract: A thorough spectral study of the intrinsic single-photon detection efficiency in superconducting TaN and NbN nanowires with different widths has been performed. The experiment shows that the cut-off of the intrinsic detection efficiency at near-infrared wavelengths is most likely controlled by the local suppression of the barrier for vortex nucleation around the absorption site. Beyond the cut-off quasi-particle diffusion in combination with spontaneous, thermally activated vortex crossing explains the detection process. For both materials, the reciprocal cut-off wavelength scales linearly with the wire width where the scaling factor agrees with the hot-spot detection model.

Abstract: We experimentally study timing jitter of single-photon detection by NbN superconducting strips with width w ranging from 190 nm to 3μm. We find that timing jitter of both narrow (190 nm) and micron-wide strips is about 40 ps at currents where internal detection efficiency η saturates and it is close to our instrumental jitter. We also calculate intrinsic timing jitter in wide strips using the modified time-dependent Ginzburg-Landau equation coupled with a two-temperature model. We find that with increasing width the intrinsic timing jitter increases and the effect is most considerable at currents where a rapid growth of η changes to saturation. We relate it with complicated vortex and antivortex dynamics, which depends on a photon’s absorption site across the strip and its width. The model also predicts that at current close to depairing current the intrinsic timing jitter of a wide strip could be about ℏ/kBTc (Tc is a critical temperature of superconductor), i.e., the same as for a narrow strip.

Abstract: Optical-to-electrical conversion, which is the basis of the operation of optical detectors, can be linear or nonlinear. When high sensitivities are needed, single-photon detectors are used, which operate in a strongly nonlinear mode, their response being independent of the number of detected photons. However, photon-number-resolving detectors are needed, particularly in quantum optics, where n-photon states are routinely produced. In quantum communication and quantum information processing, the photon-number-resolving functionality is key to many protocols, such as the implementation of quantum repeaters1 and linear-optics quantum computing2. A linear detector with single-photon sensitivity can also be used for measuring a temporal waveform at extremely low light levels, such as in long-distance optical communications, fluorescence spectroscopy and optical time-domain reflectometry. We demonstrate here a photon-number-resolving detector based on parallel superconducting nanowires and capable of counting up to four photons at telecommunication wavelengths, with an ultralow dark count rate and high counting frequency.

Abstract: We present our recent results in research and development of superconducting single-photon detector (SSPD). We achieved the following performance improvement: first, we developed and characterized SSPD integrated in optical cavity and enabling its illumination from the face side, not through the substrate, second, we improved the quantum efficiency of the SSPD at around 3 μm wavelength by reduction of the strip width to 40 nm, and, finally, we improved the detection efficiency of the SSPD-based single-photon receiver system up to 20% at 1550 nm and extended its wavelength range beyond 1800 nm by the usage of the fluoride ZBLAN fibres.

Abstract: By embedding superconducting nanowire single-photon detectors (SNSPDs) in nanophotonic circuits, these waveguide-integrated detectors are a key building block for future on-chip quantum computing applications.

Abstract: We present an extensive set of data on nanowire-type superconducting single-photon detectors based on niobium-nitride (NbN) to establish the empirical correlation between performance and the normal-state resistance per square. We focus, in particular, on the bias current, compared to the expected depairing current, needed to achieve a near-unity detection efficiency for photon detection. The data are discussed within the context of a model in which the photon energy triggers the movement of vortices i.e. superconducting dissipation, followed by thermal runaway. Since the model is based on the non-equilibrium theory for conventional superconductors deviations may occur, because the efficient regime is found when NbN acts as a marginal superconductor in which long-range phase coherence is frustrated.

Abstract: We have found experimentally that the rise time of voltage pulse in NbN superconducting single photon detectors increases nonlinearly with increasing the length of the detector L. The effect is connected with dependence of resistance of the detector Rn, which appears after photon absorption, on its kinetic inductance Lk and, hence, on the length of the detector. This conclusion is confirmed by our calculations in the framework of two temperature model.
D.Yu.V. acknowledges the support from the Russian Foundation for Basic Research (Project No. 15-42-02365). K.V.S. acknowledges the financial support from the Ministry of Education and Science of the Russian Federation (Contract No. 3.2655.2014/K).

Abstract: We present our progress on the research and development of NbN superconducting single‐photon detectors (SSPD's) for ultrafast counting of near‐infrared photons for secure quantum communications. Our SSPD's operate in the quantum detection mode based on the photon‐induced hotspot formation and subsequent development of a transient resistive barrier across an ultrathin and submicron‐width superconducting stripe. The devices are fabricated from 4‐nm‐thick NbN films and kept in the 4.2‐ to 2‐K temperature range. The detector experimental quantum efficiency in the photon‐counting mode reaches above 40% for the visible light and up to 30% in the 1.3‐ to 1.55‐µm wavelength range with dark counts below 0.01 per second. The experimental real‐time counting rate is above 2 GHz and is limited by our readout electronics. The SSPD's timing jitter is below 18 ps, and the best‐measured value of the noise‐equivalent power (NEP) is 5 × 10–21 W/Hz1/2 at 1.3 µm. In terms of quantum efficiency, timing jitter, and maximum counting rate, our NbN SSPD's significantly outperform semiconductor avalanche photodiodes and photomultipliers in the 1.3‐ to 1.55‐µm range.

Abstract: This Letter presents, to the best of our knowledge, a novel optical configuration for direct time-resolved measurements of luminescence from singlet oxygen, both in solutions and from cultured cells on photodynamic therapy. The system is based on the superconducting single-photon detector, coupled to the confocal scanner that is modified for the near-infrared measurements. The recording of a phosphorescence signal from singlet oxygen at 1270 nm has been done using time-correlated single-photon counting. The performance of the system is verified by measuring phosphorescence from singlet oxygen generated by the photosensitizers commonly used in photodynamic therapy: methylene blue and chlorin e6. The described system can be easily upgraded to the configuration when both phosphorescence from singlet oxygen and fluorescence from the cells can be detected in the imaging mode. Thus, co-localization of the signal from singlet oxygen with the areas inside the cells can be done.

Abstract: We demonstrate experimentally that single-photon detection can be achieved in micrometer-wide NbN bridges, with widths ranging from 0.53 to 5.15  μm and for photon wavelengths of 408 to 1550 nm. The microbridges are biased with a dc current close to the experimental critical current, which is estimated to be about 50% of the theoretically expected depairing current. These results offer an alternative to the standard superconducting single-photon detectors, based on nanometer-scale nanowires implemented in a long meandering structure. The results are consistent with improved theoretical modeling based on the theory of nonequilibrium superconductivity, including the vortex-assisted mechanism of initial dissipation.

Abstract: We report on the characterization of a superconducting nanowire detector for ions at low kinetic energies. We measure the absolute single-particle detection efficiency eta and trace its increase with energy up to eta = 100%. We discuss the influence of noble gas adsorbates on the cryogenic surface and analyze their relevance for the detection of slow massive particles. We apply a recent model for the hot-spot formation to the incidence of atomic ions at energies between 0.2 and 1 keV. We suggest how the differences observed for photons and atoms or molecules can be related to the surface condition of the detector and we propose that the restoration of proper surface conditions may open a new avenue for SSPD-based optical spectroscopy on molecules and nanoparticles.

Abstract: A novel superconducting single-photon detector (SSPD), intrinsically capable of high quantum efficiency (up to 20%) over a wide spectral range (ultraviolet to infrared), with low dark counts (<1 cps), and fast (<40 ps) timing resolution, is described. This SSPD has been used to perform timing measurements on complementary metal–oxide–semiconductor integrated circuits (ICs) by detecting the infrared light emission from switching transistors. Measurements performed from the backside of a 0.13 μm geometry flip–chip IC are presented. Other potential applications for this detector are in telecommunications, quantum cryptography, biofluorescence, and chemical kinetics.

Abstract: In the original paper1the Ref. 10 should be M. Sanzaro, N. Calandri, A. Ruggeri, C. Scarcella, G. Boso, M. Buttafava, and A. Tosi, Proc. SPIE9370, 93701T (2015).

Abstract: This paper highlights a significant advance in time-of-flight depth imaging: by using a scanning transceiver which incorporated a free-running, low noise superconducting nanowire single-photon detector, we were able to obtain centimeter resolution depth images of low-signature objects in daylight at stand-off distances of the order of one kilometer at the relatively eye-safe wavelength of 1560 nm. The detector used had an efficiency of 18% at 1 kHz dark count rate, and the overall system jitter was ~100 ps. The depth images were acquired by illuminating the scene with an optical output power level of less than 250 µW average, and using per-pixel dwell times in the millisecond regime.

Abstract: We study photon count statistics in superconducting single-photon detectors consisting of up to 70 narrow superconducting strips connected in parallel. Using interarrival time analysis, we demonstrate that our samples are operated in the “arm-trigger” regime and require up to seven subsequently absorbed photons to form a resistive state in the whole sample. We also performed numerical simulation of the light and dark count rates versus detector bias current, which are in good agreement with the experimental results.

Abstract: Представлены результаты исследований сверхпроводящих однофотонных детекторов, изготовленных из ультратонкой пленки NbN. Развитие технологического процесса изготовления детекторов, а также снижение рабочей температуры до 2 К позволили существенно увеличить квантовую эффективность: для видимого света (λ = 0.56 мкм) она составила 30%–40%, т.е. достигла предела, определяемого коэффициентом поглощения пленки. С ростом длины волны квантовая эффективность экспоненциально падает, составляя ~20% на λ=1.55 мкм и ~0.02% на λ = 5 мкм. При скорости темнового счета ~10-4s-1 экспериментально измеренная эквивалентная мощность шума составила 1.5 × 10-20 Вт/Гц-1/2; в дальнейшем она может быть уменьшена до рекордно низкого значения 5 × 10-21 Вт/Гц-1/2. Временное разрешение детектора равно 30 пс.

Abstract: We investigate how the bias current affects the hot-spot relaxation dynamics in niobium nitride. We use for this purpose a near-infrared pump-probe technique on a waveguide-integrated superconducting nanowire single-photon detector driven in the two-photon regime. We observe a strong increase in the picosecond relaxation time for higher bias currents. A minimum relaxation time of (22 +/- 1)ps is obtained when applying a bias current of 50% of the switching current at 1.7 K bath temperature. We also propose a practical approach to accurately estimate the photon detection regimes based on the reconstruction of the measured detector tomography at different bias currents and for different illumination conditions.

Abstract: The interest in single-photon detectors in the near-infrared wavelength regime for applications, e.g. in quantum cryptography has immensely increased in the last years. Superconducting nanowire single-photon detectors (SNSPD) already show quite reasonable detection efficiencies in the NIR which can even be further improved. Novel theoretical approaches including vortex-assisted photon counting state that the detection efficiency in the long wavelength region can be enhanced by the detector geometry and an applied magnetic field. We present spectral measurements in the wavelength range from 350-2500 nm of the detection efficiency of meander-type TaN and NbN SNSPD with varying nanowire line width from 80 to 250 nm. Due to the used experimental setup we can accurately normalize the measured spectra and are able to extract the intrinsic detection efficiency (IDE) of our detectors. The results clearly indicate an improvement of the IDE depending on the wire width according to the theoretic models. Furthermore we experimentally found that the smallest detectable photon-flux can be increased by applying a small magnetic field to the detectors.

Abstract: We fabricated and characterized nanowire superconducting single-photon detectors made of 4 nm thick amorphous Mox Si1−x films. At 1.7 K the best devices exhibit a detection efficiency (DE) up to 18% at 1.2 $\mu {\rm m}$ wavelength of unpolarized light, a characteristic response time of about 6 ns and timing jitter of 120 ps. The DE was studied in wavelength range from 650 nm to 2500 nm. At wavelengths below 1200 nm these detectors reach their maximum DE limited by photon absorption in the thin MoSi film.