Superconducting Nanowire Single-photon Detectors Research Articles

Extremely fast vortex dynamics in Bi2Sr2Ca2Cu3O10+δ crystalline nanostrip

The maximum velocity of a mobile vortex in movement is generally limited by the phenomenon of flux-flow instability (FFI), which necessitates weak vortex pinning and fast heat removal from non-equilibrium electrons. We here demonstrate exfoliations and nano-fabrications of Bi2Sr2Ca2Cu3O10+δ crystalline nanostrips, which possess a rather weak pinning volume of vortices, relatively low resistivity, and large normal electron diffusion coefficient. The deduced vortex velocity in Bi2Sr2Ca2Cu3O10+δ crystalline nanostrips can be up to 300 km/s near the superconducting transition temperature, well above the speed of sound. The observed vortex velocity is an order of magnitude faster than that of conventional superconducting systems, representing a perfect platform for exploration of ultra-fast vortex matter and a good candidate for fabrications of superconducting nanowire single photon detectors or superconducting THz modulator.

Polarizer-free measurement of the full Stokes vector using a fiber-coupled superconducting nanowire single photon detector with a polarization extinction ratio of ∼2.

The characterization and manipulation of polarization state at single photon level are of great importance in research fields such as quantum information processing and quantum key distribution, where photons are normally delivered using single mode optical fibers. To date, the demonstrated polarimetry measurement techniques based on a superconducting nanowire single photon detector (SNSPD) require the SNSPD to be either highly sensitive or highly insensitive to the photon's polarization state, therefore placing an unavoidable challenge on the SNSPD's design and fabrication processes. In this article, we present the development of an alternative polarimetry measurement technique, of which the stringent requirement on the SNSPD's polarization sensitivity is removed. We validate the proposed technique by a rigorous theoretical analysis and comparisons of the experimental results obtained using a fiber-coupled SNSPD with a polarization extinction ratio of ∼2 to that obtained using other well-established known methods. Based on the full Stokes data measured by the proposed technique, we also demonstrate that at the single photon level (∼ -100 dBm), the polarization state of the photon delivered to the superconducting nanowire facet plane can be controlled at will using a further developed algorithm. Note that other than the fiber-coupled SNSPD, the only component involved is a quarter-wave plate (no external polarizer is necessary), which when aligned well has a paid insertion loss less than 0.5 dB.

Stratospheric aerosol lidar with a 300 µm diameter superconducting nanowire single-photon detector at 1064 nm.

Stratospheric aerosols play an important role in the atmospheric chemical and radiative balance. To detect the stratospheric aerosol layer, a 1064 nm lidar with high resolution and large dynamic range is developed using a superconducting nanowire single-photon detector (SNSPD). Measurements are typically performed at 1064 nm for its sensitivity to aerosol, whereas detectors are limited by low efficiency and high dark count rate (DCR). SNSPDs are characterized by high efficiency in the infrared wavelength domain, as well as low noise and dead time, which can significantly enhance the signal quality. However, it is still challenging to build an SNSPD with both large active area and high count rate. To improve the maximal count rate (MCR) so as to avoid saturation in the near range, a 16-pixel interleaved SNSPD array and a multichannel data acquisition system are developed. As a reference, a synchronous system working at 532 nm is applied. In a continuous comparison experiment, backscatter ratio profiles are retrieved with resolutions of 90 m/3 min, and the 1064 nm system shows better performance, which is sensitive to aerosols and immune to the contamination of the ozone absorption and density of molecule change in the lower stratosphere.

Ultrafast quantum key distribution using fully parallelized quantum channels.

The field of quantum information processing offers secure communication protected by the laws of quantum mechanics and is on the verge of finding wider application for the information transfer of sensitive data. To improve cost-efficiency, extensive research is being carried out on the various components required for high data throughput using quantum key distribution (QKD). Aiming for an application-oriented solution, we report the realization of a multichannel QKD system for plug-and-play high-bandwidth secure communication at telecom wavelengths. We designed a rack-sized multichannel superconducting nanowire single photon detector (SNSPD) system, as well as a highly parallelized time-correlated single photon counting (TCSPC) unit. Our system is linked to an FPGA-controlled QKD evaluation setup for continuous operation, allowing us to achieve high secret key rates using a coherent-one-way protocol.

Fractal superconducting nanowire single-photon detectors working in dual bands and their applications in free-space and underwater hybrid LIDAR.

We demonstrate a fiber-coupled fractal superconducting nanowire single-photon detector (SNSPD) system with minimum polarization dependence of detection efficiency. Its system detection efficiency (SDE) was maximized at the wavelength of 1540 nm, which was measured to be 91 ± 4%; furthermore, we observed the second local maximum of SDE at the wavelength of 520 nm, which was measured to be 61 ± 2%. This dual-band feature of SDE was due to the enhancement of the optical absorptance by two longitudinal resonance modes of the micro-cavity. By using high SDE with minimum polarization dependence in these two bands, we implemented a hybrid LIDAR for imaging the remote objects in free space and under water.

Miniaturized superconducting single-photon detection system for airborne platform

<sec>Facing the demand for applications such as wide-area terrain mapping and space-based atmospheric measurements, there is an urgent need to develop miniaturized single-photon detection systems with low power consumption that can be adapted to airborne platforms. Superconducting nanowire single-photon detectors (SNSPDs) have been applied to quantum information, bioimaging, deep space communication and long-range lidar with the advantages of high quantum efficiency, low dark count rate and fast detection rate. However, traditional SNSPD usually operates at 2.1 K or even lower, and the required cryogenic systems are large in size and weight, which are not easy to apply to airborne platforms. Up to now, there has been no report on SNSPD applied to airborne platforms. How to apply SNSPD to airborne platforms is an urgent problem to be solved.</sec><sec>In this work, we design and make an SNSPD with an operating temperature of 4.2 K. The superconducting detector chip is a four-channel photon-number-resolving device with a photosensitive area of 60 μm × 60 μm, which is coupled to a 200-μm-diameter fiber by a beam compression system with a quantum efficiency of 50% at 1064 nm and a temperature of 4.2 K. Finally, the time characteristics of a single channel are tested in response to different photon numbers. The timing jitter of four-photon response is smallest, and the half-height width is 110 ps. This work not only supports airborne applications, but also has positive implications for promoting the development of general-purpose miniaturized SNSPD systems and their applications.</sec>

High comprehensive performance superconducting nanowire single photon detector

Superconducting nanowire single photon detector (SNSPD) has been widely used in quantum communication, quantum computing and other fields because of its excellent timing jitter and response speed. However, due to the mutual restraint of the technical parameters of SNSPD nanowires, there are technical challenges to further improve the comprehensive performance of SNSPD, and thus limiting its application on a large scale. Combining high detection efficiency with high timing performance is still an outstanding challenge. In this work, we report the SNSPD with 12-μm small active area, which has high speed, high efficiency, low jitter and broadband absorption. Au/SiO<sub>2</sub> membrane cavity, which is determined by finite element analysis simulation, is used to widen the optical response bandwidth. And it is easier to process and improve the alignment accuracy at the same time. The flat substrate is more conducive to the growth of superconducting thin films, so flattening process is introduced. Device package is also optimized to match smaller detector. Self-aligned packaging makes optical alignment more convenient and time-saving. Special optical fibers with small mode-field diameters can reduce the negative effect of the detector on optical coupling. The detector can achieve a maximum SDE of 82% at the central wavelength of 1310 nm and the temperature of 2.2 K, and the SDE of more than 65% in the wavelength range of 1200–1600 nm, with DCR of 70 cps. The detector also exhibits a count rate of 40 MHz@3 dB and a timing jitter of 38 ps, which is significantly improved compared with 23-μm active area detector. Furthermore, the minimum timing jitter of 22 ps can be obtained by using cryogenic amplifier readout. In this work, high comprehensive performance detector is developed, which provides an important technical reference for practical and product SNSPD.

Space Debris Laser Ranging with range-gate-free Superconducting Nanowire Single-Photon Detector

Space Debris Laser Ranging (DLR) is a technique to measure range to defunct satellites, rocket bodies or other space targets in orbits around Earth. The analysis shows that one of the reasons for the low success probability of DLR is the inaccurate orbital prediction of targets. Then it is proposed to use the Superconducting Nanowire Single-Photon Detector (SNSPD) running in automatic-recoverable range-gate-free mode, in which case, the effect of the accuracy of the target’s orbital prediction on the success probability of DLR is greatly reduced. In this way, 249 space debris were successfully detected and 532 passes of data were obtained. The smallest target detected was the space-debris (902) with an orbital altitude of about 1000 km and a Radar Cross Section (RCS) of 0.0446 m2. The farthest target detected was the space-debris (12,445) with a large elliptical orbit and an RCS of 18.2505 m2, of which the range of the normal point (NPT) of the measured arc-segment on January 27, 2019 was 6260.805 km.

Design and fabrication of the superconducting single-photon detector operating at the 5 - 10 micrometer wavelength band

High-performance mid-wave and long-wave infrared single-photon detectors not only have significant research value in the fields of infrared astronomy and defense technology, but are also challenging to be realized in the field of single-photon detection technology. Superconducting nanowire single-photon detectors (SNSPDs) have shown excellent performance in the near-infrared band. However, how to further improve the cutoff wavelength <i>λ</i><sub>c</sub> is a topic of widespread concern. In this paper, the method for improving <i>λ</i><sub>c</sub> by applying the regulation of the superconducting disorder is discussed, and a detector with an operating wavelength band of 5 - 10 μm is designed and fabricated. <br>Studies have shown that the multiplication and diffusion behaviors of the quasiparticles always occur during the photon detection events, although the microscopic photodetection mechanism of SNSPD still lacks a perfect theoretical explanation. Therefore, the theoretical analysis mainly considers the influence of the quasiparticles in this paper, and the mathematical formula of the detection cutoff wavelength <i>λ</i><sub>c</sub> can be obtained based on the phenomenological quasiparticle diffusion model. Furthermore, the disorder-dependent superconducting phase transition temperature <i>T</i><sub>c</sub>, superconducting energy gap <i><teshuzifu>D</i>, and electron thermalization time <i>τ</i><sub>th</sub> are also considered, in order to get more precise results.<br>Theoretical analysis suggests that the increase in the sheet resistance <i>R</i><sub>s</sub>, which evaluates the disorder strength, will help to increase <i>λ</i><sub>c</sub>. For example, when the nanowire width is kept at 30 nm and <i>R</i><sub>s</sub> > 380 Ω/□, it can be deduced that <i>λ</i><sub>c</sub> is larger than 10 μm.<br>Experimentally, the active area of the device consists of a straight superconducting nanowire with a length of 10 μm and a width of 30 nm, so that it can effectively reduce the probability of the defects on the nanowire and avoid the current crowding effect. We have fabricated a 30 nm-wide Mo<sub>0.8</sub>Si<sub>0.2</sub> mid infrared SNSPD, which has a cutoff wavelength <i>λ</i><sub>c</sub> no more than 5 μm, the effective strength of the disorder - the film sheet resistance <i>R</i><sub>s</sub> = 248.6 Ω/□. As a comparison, the sheet resistance, which is controlled by the film thickness, is increased to about 320 Ω/□ in this experiment.<br>It is demonstrated that the Mo<sub>0.8</sub>Si<sub>0.2</sub> detector with <i>R</i><sub>s</sub> ~320 Ω/□ can achieve saturated quantum efficiency at a wavelength of 6 μm. Furthermore, 53% quantum efficiency at the wavelength of 10.2 μm can be obtained when the detector works at a bias current of 0.9 <i>I</i><sub>SW</sub> (<i>I</i><sub>SW</sub> is the superconducting transition current), and it can theoretically reach a maximum value of 92% if the compression of switching current is excluded. Therefore, it can be predicted that the disorder regulation may become another efficient approach for designing high-performance mid-wave and long-wave infrared SNSPDs, in addition to the optimization of the superconducting energy gap and the cross section of superconducting nanowire.<br>However, the continuous increase in the disorder will cause a decrease in both the superconducting phase transition temperature <i>T</i><sub>c</sub> and <i>I</i><sub>SW</sub> of the detector from the point of detector fabrication and application. This downward trend is especially pronounced when the nanowire width is ultranarrow, which is not conducive to the signal readout of the detector. Thus, exploring the optimal disorder regulation technology and balancing the relationship between the operating temperature, the signal-to-noise ratio, and the cutoff wavelength will have key scientific and application value for the development of high-performance mid-wave and long-wave infrared SNSPDs.

An On-Chip Photon-Counting Reconstructive Spectrometer with Tailored Cascaded Detector Array

The hybrid integration of superconducting nanowire single-photon detectors (SNSPDs) on various substrates and photonic structures has great potential on developing complicated photonic devices based on single-photon detections, such as photon-counting reconstructive spectrometers for the spectral sensing of single-photon level faint light. In this paper, we introduce the cascaded absorption effect of SNSPDs to develop a photon-counting reconstructive spectrometer. The device includes a Rowland grating as the spatial dispersion element and a tailored cascaded SNSPD array in the focusing region of the grating. The spectral responses of the SNSPDs could be flexibly modulated by their coiled patterns and the cascaded absorption in the array, which are used as the bases for spectral reconstruction. A prototype device was designed and fabricated to demonstrate the principle of the scheme. The experiment results showed the feasibility of the spectral response modulations by the coiled pattern design and the cascaded absorption effect of the SNSPD array. It supports the spectral measurement and reconstruction in the wavelength range of 1,495 to 1,515 nm, with a spectral resolution of 0.4 nm. The proposed scheme achieves the bases for spectral reconstruction only by the design of SNSPDs and without the spectral modulation effects of additional photonic structures. It provides an interesting and promising way to develop devices with high photon utilization.

Superconducting single-photon detectors in the mid-infrared for physical chemistry and spectroscopy.

Applications of vibrational spectroscopy throughout the field of physical chemistry are limited by detectors with poor temporal resolution, low detection efficiency, and high background levels. Up to now, the field has relied upon detectors based on semiconducting materials with small bandgaps, which unavoidably leads to a compromise between good spectral response and noise at long wavelengths. However, a revolution in mid-infrared light detection is underway based on the interactions of photons with superconducting materials, which function under fundamentally different operating principles. Superconducting detectors were first used to detect light at shorter wavelengths. However, recent developments in their sensitivity toward mid-infrared wavelengths up to 10 μm provide new opportunities for applications in molecular science, such as infrared emission experiments, exoplanet spectroscopy and single molecule microscopy. In this tutorial review, we provide background information needed for the non-expert in superconducting light detection to apply these devices in the field of mid-infrared molecular spectroscopy. We present and compare the detection mechanisms and current developments of three types of superconducting detectors: superconducting nanowire single-photon detectors (SNSPDs), transition edge sensors (TESs), and microwave kinetic inductance detectors (MKIDs). We also highlight existing applications of SNSPDs for laser-induced infrared fluorescence experiments and discuss their potential for other molecular spectroscopy applications. Ultimately, superconducting infrared detectors have the potential to approach the sensitivity and characteristics of established single-photon detectors operating in the UV/Vis region, which have existed for almost a century and become an indispensable tool within the field of physical chemistry.

The dependence of timing jitter of superconducting nanowire single-photon detectors on the multi-layer sample design and slew rate.

We investigated the timing jitter of superconducting nanowire single-photon detectors (SNSPDs) and found a strong dependence on the detector response. By varying the multi-layer structure, we observed changes in pulse shape which are attributed to capacitive behaviour affecting the pulse heights, rise times and consequently timing jitter. Moreover, we developed a technique to predict the timing jitter of a single device within certain limits by capturing only a single detector pulse, eliminating the need for detailed jitter measurement using a pulsed laser when a rough estimate of the timing jitter is sufficient.

Nanosecond gating of superconducting nanowire single-photon detectors using cryogenic bias circuitry.

Superconducting nanowire single-photon detectors (SNSPDs) show near unity efficiency, low dark count rate, and short recovery time. Combining these characteristics with temporal control of SNSPDs broadens their applications as in active de-latching for higher dynamic range counting or temporal filtering for pump-probe spectroscopy or LiDAR. To that end, we demonstrate active gating of an SNSPD with a minimum off-to-on rise time of 2.4 ns and a total gate length of 5.0 ns. We show how the rise time depends on the inductance of the detector in combination with the control electronics. The gate window is demonstrated to be fully and freely, electrically tunable up to 500 ns at a repetition rate of 1.0 MHz, as well as ungated, free-running operation. Control electronics to generate the gating are mounted on the 2.3 K stage of a closed-cycle sorption cryostat, while the detector is operated on the cold stage at 0.8 K. We show that the efficiency and timing jitter of the detector is not altered during the on-time of the gating window. We exploit gated operation to demonstrate a method to increase in the photon counting dynamic range by a factor 11.2, as well as temporal filtering of a strong pump in an emulated pump-probe experiment.

Adsorption behavior of transition metal (Pd, Pt, Ag and Au) doped SnS monolayers on SF6 decomposed species and the effects of applied electric field and biaxial strain

The adsorption behavior of SF6 characteristic decomposition products (SO2 and SOF2) on intrinsic and transition metal (TM) atom modified SnS monolayers is investigated based on the first principles. The adsorption structure, adsorption energy, density of states, electron localization function, electron density difference, work function, and desorption properties are discussed to evaluate SnS monolayers as potential candidates as adsorbents for SO2 and SOF2. Our results show that the detection performance of the intrinsic SnS monolayer is poor due to the relatively weak interaction with gas molecules. After introducing TM dopants (TM = Pd, Pt, Ag and Au) on SnS monolayer, Pd and Pt atoms tend to be adsorbed on TH sites, while Ag and Au atoms are more easily captured by TS sites. The results of adsorption energy and electronic properties showed that TM atoms could significantly improve the adsorption properties of SO2 and SOF2 molecules on SnS monolayers. Furthermore, the effects of electric field and biaxial strain on the sensing properties of gas molecules on TM-SnS monolayers are also investigated. Finally, the desorption time of gas molecules from the TM-SnS monolayer is estimated to evaluate its potential application in the detection and removal of faulty gases in SF6 power devices. The research results not only reveal the sensing mechanism of the TM-SnS monolayer for the characteristic decomposition products of SF6, but also provide theoretical guidance for the further development of SnS-based adsorbents or scavengers.

Local-Scale Horizontal CO2 Flux Estimation Incorporating Differential Absorption Lidar and Coherent Doppler Wind Lidar

A micro-pulse lidar system incorporating differential absorption lidar (DIAL) and coherent Doppler wind lidar (CDWL) is proposed and demonstrated. Due to the high signal-to-noise ratio (SNR) of the superconducting nanowire single-photon detector (SNSPD), the DIAL channel achieves high sensitivity in CO2 measurement. Meanwhile, the CDWL channel is used to obtain the horizontal wind field. In the process of the optimization and calibration of the DIAL receiver, specifically, mode scrambling and temperature control of the connecting fiber between the telescope and the SNSPD enhance the stability and robustness of the system. Horizontal scanning of the CO2 concentration and the wind field is carried out in a 6 km range over a scanning span of 60° with a radial resolution of 150 m and 15 s. The results show that the hybrid lidar system captures the spatial distribution of CO2 concentration and the wind field simultaneously. The horizontal net CO2 flux in a radius of 6 km is estimated by integrating the CO2 concentration and the wind transport vector, indicating different characteristics of horizontal net CO2 fluxes in an industrial area, a university campus, and a park. During most of the experiment, CO2 flux remained positive in the industrial area, but balances fell to nearly zero on the campus and in the park. The horizontal net fluxes averaged over 24 h in the three areas are 3.5 × 105 ppm·m2·s−1, 0.7 × 105 ppm·m2·s−1, and 0.1 × 105 ppm·m2·s−1.

Mid-infrared Nb4N3-based superconducting nanowire single photon detectors for wavelengths up to 10 µm.

Mid-infrared (MIR) single-photon detection is emerging as an important technology for various applications. Superconducting nanowire single photon detectors (SNSPDs) fabricated with superconducting films with energy gaps of a few meV are natural broadband single-photon detectors. Recently, extending SNSPDs' operation wavelengths into the MIR region is highly attractive. γ-Nb4N3 has a reduced N content and lower energy gap than the commonly used δ-NbN, making SNSPDs based on γ-Nb4N3 film more sensitive to low energy photons. We report on a Nb4N3-SNSPD based on 62-nm wide nanowire, with an optical absorption enhancement design and an optimized device package for efficient ZBLAN fiber coupling and dark count filtering. The developed device has a unity intrinsic detection efficiency (IDE) in the 1.5-4 µm wavelength region, and the device detection efficiency at 2.95 µm was measured to be 32.5%, with an uncertainty of 12.7%. Furthermore, we reduced the device geometry, and measured 3-10 µm photon response of a device based on 5-nm film and 42-nm nanowire, with an IDE of 95%, 81%, 40%, and 6% for 4.8, 6, 8, and 10 µm, respectively.

Performance of an Asymmetric on–Off Keying Modulation for Space Communications Using Single-Photon Superconducting Nanowire Detectors

Communications from deep space need to overcome two major issues: the strong attenuation due to the large distances and the limited power available at the transmitter. A class of sensors which looks promising for deep space communications is provided by the superconducting nanowire single-photon detectors that are characterized by very small jitter (few tens of ps), fast rise (hundreds of ps), and comparatively slow decay (few ns). Although it could seem that the bottleneck is represented by the long reset time, in this article, we present a scheme whose effective rate is limited by the jitter and that is able to transmit, with a superconducting nanowire single-photon detector with a ratio between decay time and jitter equal to 170 (a typical value), almost six times faster than the rate that the decay time would allow.

Fully integrated four-channel wavelength-division multiplexed QKD receiver

Quantum key distribution (QKD) enables secure communication even in the presence of advanced quantum computers. However, scaling up discrete-variable QKD to high key rates remains a challenge due to the lossy nature of quantum communication channels and the use of weak coherent states. Photonic integration and massive parallelization are crucial steps toward the goal of high-throughput secret-key distribution. We present a fully integrated photonic chip on silicon nitride featuring a four-channel wavelength-division demultiplexed QKD receiver circuit including state-of-the-art waveguide-integrated superconducting nanowire single-photon detectors (SNSPDs). With a proof-of-principle setup operated at a clock rate of 3.35 GHz, we achieve a total secret-key rate of up to 12.17 Mbit/s at 10 dB channel attenuation with low detector-induced error rates. The QKD receiver architecture is massively scalable and constitutes a foundation for high-rate many-channel QKD transmission.

Fast and accurate measurement of the polarization-dependent detection efficiency of superconducting nanowire single photon detectors.

Superconducting nanowire single photon detectors (SNSPDs) have been extensively investigated due to their superior characteristics, including high system detection efficiency, low dark count rate and short recovery time. The polarization sensitivity introduced by the meandering-type superconductor nanowires is an intrinsic property of SNSPD, which is normally measured by sweeping hundreds of points on the Poincaré sphere to overcome the unknown birefringent problem of the SNSPD's delivery fiber. In this paper, we propose an alternative method to characterize the optical absorptance of SNSPDs, without sweeping hundreds of points on the Poincaré sphere. It is shown theoretically that measurements on the system detection efficiencies (SDEs) subject to cases of four specific photon polarization states are sufficient to reveal the two eigen-absorptances of the SNSPD. We validate the proposed method by comparing the measured detection spectra with the spectra attained from sweeping points on the Poincaré sphere and the simulated absorption spectra.

Stacking two superconducting nanowire single-photon detectors via membrane microchip transfer

Multilayer superconducting nanowire single-photon detectors (SNSPDs) have exhibited several advantages, such as increased detection efficiency, reduced polarization sensitivity, and scaling up to large arrays. However, monolithic fabrication of such multilayer devices is challenging. In this work, a hybrid integration method has been introduced by etching SNSPDs into the membrane microchips, followed by the pick and place transferring process. This method has been verified by stacking two SNSPDs orthogonally. Both detectors show near saturated detection efficiencies and low timing jitters. Furthermore, thermal coupling effects have been observed between the two SNSPDs. The photon detection pulses from either detector can trigger the other one almost deterministically with a latency of several nanoseconds. This method offers a flexible way to fabricate multilayer SNSPDs or integrate them with other heterogeneous devices.