Single-photon Detector Technology Research Articles

Impact of visibility limiting conditions on satellite and high-altitude platform quantum key distribution links.

Satellite and aerial platforms are critical in the deployment of global quantum communications networks. Currently, there remain significant challenges including operation during daytime and robustness to visibility limiting conditions. In this work we investigate, through simulation, the impact of visibility limiting conditions on low-Earth orbit CubeSat dimensioned satellites, small satellites and high-altitude platform implementations. Three different operational wavelengths were considered: currently used near-infrared (at 850 nm); next-generation short-wave infrared (at 1550 nm); and a candidate longer wavelength (at 2133 nm). We present channel attenuation and consider quantum key distribution (QKD) system performance parameters. Results indicate that the "best wavelength" for an implementation depends on the minimum visibility rated and the single-photon detector technology utilized. In the cases where tolerated meteorological visibility is short, 1550 nm and 2133 nm wavelengths provide better performance. In cases when the visibility is long, the operational wavelength of 850 nm provides better QKD system performance.

Single Photon Detection Technology in Underwater Wireless Optical Communication: Modulation Modes and Error Correction Coding Analysis

Single Photon Detection Technology in Underwater Wireless Optical Communication: Modulation Modes and Error Correction Coding Analysis

Security Analysis of Differential Chaotic Keying in Optical Communication

Space free optical communication (FSO) has the advantages of wide bandwidth resources, less susceptibility to attacks, strong resistance to interference, and low losses. The FSO system itself has high security, with the realization of single photon detection technology, the stealer can obtain information without blocking the beam propagation. So using chaotic encryption methods can further improve the security performance of communication systems. This article uses a gamma gamma turbulence model and utilizes the differential chaotic shift keying (DCSK) method of communication systems to improve the system’s resistance to attacks. The theoretical expression of the system error rate under this model is derived, and the security performance of the system is further analyzed. Through experimental simulation, it is proved that the system has better resistance to attacks and lower bit error rates.

Optical–Mechanical Integration Analysis and Validation of LiDAR Integrated Systems with a Small Field of View and High Repetition Frequency

Integrated systems are facing complex and changing environments with the wide application of atmospheric LiDAR in civil, aerospace, and military fields. Traditional analysis methods employ optical software to evaluate the optical performance of integrated systems, and cannot comprehensively consider the influence of optical and mechanical coupling on the optical performance of the integrated system, resulting in the unsatisfactory accuracy of the analysis results. Optical–mechanical integration technology provides a promising solution to this problem. A small-field-of-view LiDAR system with high repetition frequency, low energy, and single-photon detection technology was taken as an example in this study, and the Zernike polynomial fitting algorithm was programmed to enable transmission between optical and mechanical data. Optical–mechanical integration technology was employed to obtain the optical parameters of the integrated system under a gravity load in the process of designing the optical–mechanical structure of the integrated system. The experimental validation results revealed that the optical–mechanical integration analysis of the divergence angle of the transmission unit resulted in an error of 2.586%. The focal length of the telescope increased by 89 μm, its field of view was 244 μrad, and the error of the detector target surface spot was 4.196%. The continuous day/night detection results showed that the system could accurately detect the temporal and spatial variations in clouds and aerosols. The inverted optical depths were experimentally compared with those obtained using a solar photometer. The average optical depth was 0.314, as detected using LiDAR, and 0.329, as detected by the sun photometer, with an average detection error of 4.559%. Therefore, optical–mechanical integration analysis can effectively improve the stability of the structure of highly integrated and complex optical systems.

A 64-pixel mid-infrared single-photon imager based on superconducting nanowire detectors.

A large-format mid-infrared single-photon imager with very low dark count rates would enable a broad range of applications in fields like astronomy and chemistry. Superconducting nanowire single-photon detectors (SNSPDs) are a mature photon-counting technology as demonstrated by their figures of merit such as high detection efficiencies and very low dark count rates. However, scaling SNSPDs to large array sizes for mid-infrared applications requires sophisticated readout architectures in addition to superconducting materials development. In this work, an SNSPD array design that combines a thermally coupled row-column multiplexing architecture with a thermally coupled time-of-flight transmission line was developed for mid-infrared applications. The design requires only six cables and can be scaled to larger array sizes. The demonstration of a 64-pixel array shows promising results for wavelengths between 3.4 μm and 10 μm, which will enable the use of this single-photon detector technology for a broad range of new applications.

PE-RASP: range image stitching of photon-efficient imaging through reconstruction, alignment, stitching integration network based on intensity image priors.

Single photon imaging integrates advanced single photon detection technology with Laser Radar (LiDAR) technology, offering heightened sensitivity and precise time measurement. This approach finds extensive applications in biological imaging, remote sensing, and non-visual field imaging. Nevertheless, current single photon LiDAR systems encounter challenges such as low spatial resolution and a limited field of view in their intensity and range images due to constraints in the imaging detector hardware. To overcome these challenges, this study introduces a novel deep learning image stitching algorithm tailored for single photon imaging. Leveraging the robust feature extraction capabilities of neural networks and the richer feature information present in intensity images, the algorithm stitches range images based on intensity image priors. This innovative approach significantly enhances the spatial resolution and imaging range of single photon LiDAR systems. Simulation and experimental results demonstrate the effectiveness of the proposed method in generating high-quality stitched single-photon intensity images, and the range images exhibit comparable high quality when stitched with prior information from the intensity images.

Retracted: Optical Fiber Multiparameter Detection and Numerical Simulation and Characteristics of Water Quality Particulate Matter Based on Single-Photon Detection Technology

Retracted: Optical Fiber Multiparameter Detection and Numerical Simulation and Characteristics of Water Quality Particulate Matter Based on Single-Photon Detection Technology

Sensing profiles of the volume scattering function at 180° using a single-photon oceanic fluorescence lidar.

A novel oceanic fluorescence lidar technique has been proposed and demonstrated for remotely sensing the volume scattering function at 180° (βf), which can be used to further retrieve the profiles of the absorption coefficient of phytoplankton (aph) at 532 nm and chlorophyll concentration (Chl). This scheme has these features. 1) The single-photon detection technology is employed to enhance the detection sensitivity to the single-photon level, enabling the oceanic lidar to obtain fluorescence backscatter profiles. 2) In terms of algorithms, the Raman backscattered signals of the water are utilized to normalize the backscattered signals of chlorophyll fluorescence, effectively minimizing the depth-dependent variation of the differential lidar attenuation coefficient (Δ K l i d a r f r). To reduce the contamination of fluorescence signals in the Raman backscatter signals, a Raman filter with a bandwidth of 6 nm was chosen. Subsequently, a perturbation method is utilized to invert the βf of the fluorescence lidar. Finally, aph and Chl profiles can be inverted based on empirical models. 3) The value of Δ K l i d a r f r used in inversion is obtained through a semi-analytic Monte Carlo simulation. According to theoretical analysis, the maximum relative error of βf for Chl ranging from 0.01 mg/m3 to 10 mg/m3 is less than 13 %. To validate this approach, a field experiment was conducted aboard the R/V Tan Kah Kee in the South China Sea from September 4th to September 5th, 2022, resulting in continuous subsurface profiles of βf, aph, and Chl. These measurements confirm the robustness and reliability of the oceanic single-photon fluorescence lidar system and the inversion algorithm.

Single-photon detection for long-range imaging and sensing

Single-photon detectors with picosecond timing resolution have advanced rapidly in the past decade. This has spurred progress in time-correlated single-photon counting applications, from quantum optics to life sciences and remote sensing. A variety of advanced optoelectronic device architectures offer not only high-performance single-pixel devices but also the ability to scale up to detector arrays and extend single-photon sensitivity into the short-wave infrared and beyond. The advent of single-photon focal plane arrays is poised to revolutionize infrared imaging and sensing. In this mini-review, we set out performance metrics for single-photon detection, assess the requirements of single-photon light detection and ranging, and survey the state of the art and prospects for new developments across semiconductor and superconducting single-photon detection technologies. Our goal is to capture a snapshot of a rapidly developing landscape of photonic technology and forecast future trends and opportunities.

Submerged single-photon LiDAR imaging sensor used for real-time 3D scene reconstruction in scattering underwater environments.

We demonstrate a fully submerged underwater LiDAR transceiver system based on single-photon detection technologies. The LiDAR imaging system used a silicon single-photon avalanche diode (SPAD) detector array fabricated in complementary metal-oxide semiconductor (CMOS) technology to measure photon time-of-flight using picosecond resolution time-correlated single-photon counting. The SPAD detector array was directly interfaced to a Graphics Processing Unit (GPU) for real-time image reconstruction capability. Experiments were performed with the transceiver system and target objects immersed in a water tank at a depth of 1.8 meters, with the targets placed at a stand-off distance of approximately 3 meters. The transceiver used a picosecond pulsed laser source with a central wavelength of 532 nm, operating at a repetition rate of 20 MHz and average optical power of up to 52 mW, dependent on scattering conditions. Three-dimensional imaging was demonstrated by implementing a joint surface detection and distance estimation algorithm for real-time processing and visualization, which achieved images of stationary targets with up to 7.5 attenuation lengths between the transceiver and the target. The average processing time per frame was approximately 33 ms, allowing real-time three-dimensional video demonstrations of moving targets at ten frames per second at up to 5.5 attenuation lengths between transceiver and target.

Quantum technologies for secure communications in space

Quantum technologies have been proved useful for space applications, such as for the well-known application of quantum key distribution (QKD). However, QKD shows a number of serious practical limitations and therefore we are interested in different ways of using quantum resources and readily available quantum technology for secure communication in space. Towards this aim, we first of all provide an overview of quantum resources and state-of-the art quantum technologies, specifically sources and detectors. Then, we identify two realistic and related applications for the short-term. The first one is quantum-enhanced communication as quantified by Shannon rates using single-photon detection technology and lasers. In this case, we show illustrative potential gains for Optical On/Off Keying (O3K) communications. The second one is quantum physical layer cryptography, which builds upon quantumenhanced communications. In this case, we show how to realize secure communication in space with quantum resources, cryptographic primitives and without the use of any key, which we call Quantum Keyless Privacy (QKP). It is a variant of the quantum wiretap channel principle hybridized with primitives and technology of QKD. In this case, we discuss the security of QKD and of our method and show that both methods provide information theoretical security.

A Compact Upconversion Single-Photon Imager for Full-Range and Accurate 3-D Imaging

The rapid development of single photon detection technology offers the possibility for an imaging system to go beyond the traditional limits. Recently, single-photon imagers based on upconversion technique have achieved unprecedentedly high resolution and noise tolerance in 3D imaging. Nevertheless, the limited imaging range, complicated optical path and long data acquisition time impose remaining challenges to practical applications. In this work, we build an upconversion single-photon imager for full-range and accurate 3D imaging. A compact all-fiber design allows our system to work robustly in an open environment. Compared to the previous imagers, the imaging speed is increased by three orders of magnitude due to the high upconversion efficiency and photon-efficient algorithm. With the application of a high-repetition laser and a nanosecond optical delay line, we achieve full-range imaging under the upconversion scheme against high solar background noise. For close-up scenes, our imager achieves ultrahigh axial resolution up to 20 μm, which is not affected by the time jitter or pileup effect of the single photon detector. Our proposal can stimulate practical applications in sophisticated scenarios.

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.

Optical Fiber Multiparameter Detection and Numerical Simulation and Characteristics of Water Quality Particulate Matter Based on Single-Photon Detection Technology

Water quality testing is of great significance for daily water use or water use in high precision manufacturing. The use of single-photon detection technology to detect water particles is one of the important methods of physical water quality detection. However, the current water quality particle detection technology needs to be improved in the range and accuracy of turbidity detection. The paper aims to use single-photon detection technology to design a fiber optic turbidity detection system to solve the current problems of small turbidity detection range and low accuracy in a large range. In response to this, this paper has made an in-depth understanding of single-photon detection technology and designed two sets of detection schemes using the performance of photons. The first set is the transmission optical fiber turbidity detection, which can effectively detect the ultralow turbidity range and a wide range of water quality particles. The second set is a scattering optical fiber turbidity detection system, which can effectively detect water particles in the low and medium turbidity range. In this paper, the two systems were integrated into a whole system, so the results of the two detection methods can also be compared, and the detected turbidity can be obtained more accurately. The experimental results showed that for the transmission optical fiber turbidity detection system, the detection effect of the system was the best under the incident light intensity of 11 wm, and the fitting value was 0.99; for the scattering optical fiber turbidity detection system, the detection effect of the system was the best under the incident light intensity of 4 wm, and the fitting value was 0.99.

Efficient mid-infrared single-photon detection using superconducting NbTiN nanowires with high time resolution in a Gifford-McMahon cryocooler

Shortly after their inception, superconducting nanowire single-photon detectors (SNSPDs) became the leading quantum light detection technology. With the capability of detecting single-photons with near-unity efficiency, high time resolution, low dark count rate, and fast recovery time, SNSPDs outperform conventional single-photon detection techniques. However, detecting lower energy single photons ( < 0.8 eV ) with high efficiency and low timing jitter has remained a challenge. To achieve unity internal efficiency at mid-infrared wavelengths, previous works used amorphous superconducting materials with low energy gaps at the expense of reduced time resolution (close to a nanosecond), and by operating them in complex milliKelvin (mK) dilution refrigerators. In this work, we provide an alternative approach with SNSPDs fabricated from 5 to 9.5 nm thick NbTiN superconducting films and devices operated in conventional Gifford-McMahon cryocoolers. By optimizing the superconducting film deposition process, film thickness, and nanowire design, our fiber-coupled devices achieved > 70 % system detection efficiency (SDE) at 2 μm and sub-15 ps timing jitter. Furthermore, detectors from the same batch demonstrated unity internal detection efficiency at 3 μm and 80% internal efficiency at 4 μm, paving the road for an efficient mid-infrared single-photon detection technology with unparalleled time resolution and without mK cooling requirements. We also systematically studied the dark count rates (DCRs) of our detectors coupled to different types of mid-infrared optical fibers and blackbody radiation filters. This offers insight into the trade-off between bandwidth and DCRs for mid-infrared SNSPDs. To conclude, this paper significantly extends the working wavelength range for SNSPDs made from polycrystalline NbTiN to 1.5–4 μm, and we expect quantum optics experiments and applications in the mid-infrared range to benefit from this far-reaching technology.

Visible-wavelength polarization-entangled photon source for quantum communication and imaging

We present a polarization-entangled photon pair source operating in the visible light range around 532 nm. Employing a collinear crossed-crystal scheme with type-I degenerate phase matching in barium borate (BBO), our source achieves a brightness of 9.5 k pairs/s/mW and a quantum state fidelity of 98.3%, making it a candidate for integration in microscopes and make use of the advantages of mid-visible optimized single-photon detection technologies. In order to study potential applications, we present a trade-off between source brightness and polarization entanglement visibility and propose use cases for different filtering configurations of the source, capable of a brightness up to 1.23 M pairs/s/mW.

Higher-order photon antibunching of phase-variable squeezed coherent state

<sec>Squeezed state has important applications in quantum communication, quantum computing, and precision measurement. It has been used to improve the sensitivity and measurement accuracy of gravitational wave detectors. Currently, squeezed state can be prepared by optical parametric oscillators, four-wave mixing, and atom–optomechanical coupling. As a typical non-classical light, the photon statistics of squeezed state usually shows obvious bunching effect, but it can also present photon antibunching effect through interference or photon subtraction operation. More importantly, squeezed coherent state is prepared by performing displacement operation on the squeezed state. In the case of certain displacement and squeezing operations, squeezed coherent state with obvious antibunching effect can be produced. The squeezed coherent state with photon antibunching effect can be employed to achieve super-resolution imaging beyond the diffraction limit, and the state exhibits good particle features which can suppress the multiphoton emission. Then it has become a focus for studying the antibunching effect and quantum statistical properties of squeezed coherent state at a single-photon level.</sec><sec>The photon antibunching effect can be characterized by the second-order photon correlation <i>g</i><sup>(2)</sup>(τ), which is introduced by Glauber to determine the non-classical properties of the light field. Namely, the second-order photon correlation <i>g</i><sup>(2)</sup> can be used as a metric to distinguish different lights. Hanbury Brown-Twiss (HBT) scheme is used to measure the second-order photon correlation experimentally. However, the second-order photon correlation <i>g</i><sup>(2)</sup> can reflect only the variance of the photon-number statistical distribution. In order to obtain more information about the photon statistical distribution and non-classical features, it is necessary to measure higher-order photon correlations. Then the higher-order photon correlations for different light fields are studied by extending the traditional HBT scheme and combining with multiplex single-photon detection technology. This method can be applied to ghost imaging, characterization of single-photon detectors, research of exciton dynamics, and analysis of NV center fluorescence emission. However, the research on photon statistics of the squeezed state focuses mainly on the second-order photon correlation and the effect of displacement amplitude on the statistical properties. The effect of squeezed phase on photon antibunching and higher-order photon correlation of squeezed coherent states, with background noise and detection efficiency taken into consideration, have not been investigated.</sec><sec>In this paper, we study high-order photon correlations and antibunching effect of phase-variable squeezed coherent state based on an extended HBT scheme. The photon statistics of the squeezed coherent state manifests prominent antibunching effect by adjusting the squeezing parameter r, displacement amplitude <i>α</i> and squeezing phase <i>θ</i>. The antibunching effect of the state can be obtained in a wide range of <i>α</i>-<i>r</i> parameter space when squeezing phase <i>θ</i>∈[0,π/2]. In an ideal case, the minimum antibunching values of the squeezed coherent state are <i>g</i><sup>(2)</sup> = 4.006 × 10<sup>–4</sup>, <i>g</i><sup>(3)</sup> = 1.3594 × 10<sup>–4</sup> and <i>g</i><sup>(4)</sup> = 6.6352 × 10<sup>–5</sup>. When the detection efficiency <i>η</i> = 0.1 and background noise <i>γ</i> = 10<sup>–6</sup>, the strong antibunching effect can still be observed, specifically, <i>g</i><sup>(2)</sup> = 0.1740, <i>g</i><sup>(3)</sup> = 0.0432, <i>g</i><sup>(4)</sup> = 0.0149. The results indicate that the antibunching effect of higher-order photon correlation has strong robustness against the experimental environment. In addition, the antibunching effect of the phase-variable squeezed coherent state is studied as a function of the measured mean photon number <<i>n</i>> and the squeezing degree S. When the measured mean photon number is much less than 1 and the squeezing parameter is less than 10<sup>–4</sup>, a prominent photon anti-bunching effect of <i>g</i><sup>(<i>n</i>)</sup> <inline-formula><tex-math id="Z-20220921173504">\begin{document}$\ll $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220574_Z-20220921173504.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="19-20220574_Z-20220921173504.png"/></alternatives></inline-formula> 0.5 can still be obtained. The results show that the control of the squeezing phase <i>θ</i> can be used to prepare the squeezed coherent state with obvious antibunching effect, which has potentially important applications in quantum metrology and secure communication.</sec>

Design and fabrication of superconducting single-photon detector operating in 5–10 μm wavelength band

<sec>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 also are the challenges in the field of single-photon detection technology. Superconducting nanowire single-photon detectors (SNSPDs) have shown excellent performances 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 of improving <i>λ</i><sub>c</sub> by regulating the superconducting disorder is discussed, and a detector with an operating wavelength band of 5–10 μm is designed and fabricated.</sec><sec>The studies show 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>Δ</i>, and electron thermalization time <i>τ</i><sub>th</sub> are also considered, in order to obtain more precise results.</sec><sec>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/square, it can be deduced that <i>λ</i><sub>c</sub> is larger than 10 μm.</sec><sec>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 fabricate 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/square. For comparison, the sheet resistance, which is controlled by the film thickness, increases to about 320 Ω/square in this experiment.</sec><sec>It is demonstrated that the Mo<sub>0.8</sub>Si<sub>0.2</sub> detector with <i>R</i><sub>s <inline-formula><tex-math id="Z-20221216014812-1">\begin{document}$ \sim $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221594_Z-20221216014812-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="24-20221594_Z-20221216014812-1.png"/></alternatives></inline-formula></sub>320 Ω/square can achieve saturated quantum efficiency at a wavelength of 6 μm. Furthermore, 53% quantum efficiency at a 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 to 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.</sec><sec>However, the continuous increase in the disorder will cause both the superconducting phase transition temperature <i>T</i><sub>c</sub> and <i>I</i><sub>SW</sub> of the detector to decrease from the viewpoint 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 among 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.</sec>

Research on photon-level ghost imaging restoration based on deep learning

In the extreme environment, the signal of the target object is very weak, even reaching the photon level. The single-photon detection technology can detect the weak signal effectively. Ghost imaging (GI) system with single-photon detection technology has a good application in weak light imaging, but the quality of the photon-level GI is still poor. In this paper, we develop a conditional generative adversarial network (CGAN) algorithm to restore images, and the network is trained with simulation data. The results show that the CGAN algorithm has an excellent performance, and the average PSNR and SSIM of test results increase to about 20.8 dB and 0.87 respectively, proving the proposed method is feasible. It is of great significance for imaging under low photon conditions.

Recent advances in superconducting nanowire single-photon detector technology for exoplanet transit spectroscopy in the mid-infrared

The Origins Space Telescope mission concept includes an exoplanet transit spectrometer that requires detector arrays with ultrahigh pixel-to-pixel stability. Superconducting nanowire single-photon detectors, or SNSPDs, have the potential to meet these stringent stability requirements due to their digital-like output. Traditionally used for applications at near-IR telecom wavelengths, SNSPDs have demonstrated near-unity detection efficiencies, ultralow dark-count rates, and high dynamic ranges. Until recently, however, SNSPD operation at the mid-infrared (mid-IR) wavelengths of interest for Origins had not been demonstrated, and SNSPD formats were limited to small arrays and active areas. Recent advances in SNSPD fabrication techniques have pushed SNSPD sensitivity to wavelengths beyond 7 μm and have enabled millimeter-scale active areas and kilopixel arrays. We report here on this progress and the outlook toward developing arrays of ultrastable superconducting nanowire single-photon detectors for mid-IR astronomy applications.