Dark Count Research Articles

Optimal Leveraging of a Gifford-McMahon Cryocooler’s Regenerative Cooling Power for SNSPD Applications

Superconducting nanowire single photon detectors (SNSPDs) offer unparalleled efficiency, minimal dark count rates, and picosecond jitter, making them ideal for single photon detector applications across the visible to mid-IR spectrum. A common cryogenic system used to reach these detectors’ optimal operating temperatures (>1 K) consists of Sumitomo’s compact RDK101 Gifford McMahon Cryocooler (GMC) running on an Zephyr air cooled compressor, coupled with a helium four (4He) adsorption stage. In this work, our aim is to provide measurements of the RDK101 GMC second stage regenerator tube cooling power at several locations along its length. We then characterise the performance of the adsorption cooler with heat loads applied to the regenerator tube. Our measurements demonstrate that heat loads of 1.2 W can be intercepted at the tube’s section near the GMC’s first cooling stage, with a negligible effect on the performance of the adsorption cooler. The thermal conductivity of yellow brass coaxial was characterised from 4 K to 40 K. Here we show that the heat load from 64 coaxial cable can be optimally intercepted with the defined regenerator cooling power. These results indicate that a 1024-pixel SNSPD array using a 32x32 row column multiplexing architecture could be successfully implemented in this cryogenic platform.

Dark Count Analysis in 4H-SiC Based UV Avalanche Photodiodes With Effective After-Pulse Suppression

Dark Count Analysis in 4H-SiC Based UV Avalanche Photodiodes With Effective After-Pulse Suppression

Free-space coupled, large-active-area superconducting microstrip single-photon detector for photon-counting time-of-flight imaging

Numerous applications at the photon-starved regime require a free-space coupling single-photon detector with a large active area, low dark count rate (DCR), and superior time resolutions. Here, we developed a superconducting microstrip single-photon detector (SMSPD), with a large active area of 260 µm in diameter, a DCR of ∼5kcps, and a low time jitter of ∼171ps, operated at a near-infrared of 1550 nm and a temperature of ∼2.0K. As a demonstration, we applied the detector to a single-pixel galvanometer scanning system and successfully reconstructed the object information in depth and intensity using a time-correlated photon counting technology.

Deterministic storage and retrieval of telecom light from a quantum dot single-photon source interfaced with an atomic quantum memory.

A hybrid interface of solid-state single-photon sources and atomic quantum memories is a long sought-after goal in photonic quantum technologies. Here, we demonstrate deterministic storage and retrieval of light from a semiconductor quantum dot in an atomic ensemble quantum memory at telecommunications wavelengths. We store single photons from an indium arsenide quantum dot in a high-bandwidth rubidium vapor-based quantum memory, with a total internal memory efficiency of (12.9 ± 0.4)%. The signal-to-noise ratio of the retrieved light field is 18.2 ± 0.6, limited only by detector dark counts.

A versatile photon counting system with active afterpulse suppression for free-running negative-feedback avalanche diodes.

InGaAs/InP-based negative-feedback avalanche diodes (NFADs) have been demonstrated to be an excellent option for photon detection at telecom wavelengths in quantum communication applications, where photon arrival times are random. However, it is well-known that the operation of NFADs at low temperatures (193K or below) is crucial to minimize the effects of afterpulsing and high dark count rates (DCRs). In this work, we present a new versatile readout electronics system with active afterpulse suppression that also offers flexible cooling options. Through the characterization of two NFAD detectors from Princeton Lightwave, Inc. and a thorough evaluation of our electronics' performance under various operating conditions, we demonstrate the effectiveness of this readout system in improving the performance of NFAD-based photon detectors. At the optimal bias for NFADs, our electronics were able to significantly reduce the afterpulsing probability by a factor of 200 for dead times ranging from 5 to 20µs following each detection event. This helps to keep the total DCRs at around 100 counts per second or less for a 20µs hold-off time. The versatility of our detection system makes NFADs a cost-effective alternative to more complex detectors, such as superconducting nanowire single-photon detectors, in the research of long-distance quantum communications and low-noise single photon detectors at telecommunication wavelengths.

Noise-resilient single-pixel compressive sensing with single photon counting

The fast expansion of photon detection technology has fertilized the rapid growth of single-photon sensing and imaging techniques. While promising significant advantages over their classical counterparts, they suffer from ambient and quantum noises whose effects become more pronounced at low light levels, limiting the quality of the acquired signal. Here, we study how photon-counting noises degrade a single-pixel optical classifier via compressive sensing, and how its performance can be restored by using quantum parametric mode sorting. Using modified National Institute of Standards and Technology (MNIST) handwritten digits as an example, we examine the effects of detector dark counts and in-band background noises and demonstrate the effectiveness of mode filtering and upconversion detection in addressing those issues. We achieve 94% classification accuracy in the presence of 500 times stronger in-band noise than the signal received. Our results suggest a robust and efficient approach to single photon sensing in a practical environment, where sunlight, ambient, and multiscattering noises can easily dominate the weak signal.

Waveform simulation in PandaX-4T* *This work was supported in part by the National Science Foundation of China (12090060, 12090061), Ministry of Science and Technology of China (2023YFA1606200), and Office of Science and Technology, Shanghai Municipal Government (22JC1410100). We are thankful for the support provided by the Double First Class Plan of the Shanghai Jiao Tong University and Guangzhou Municipal Science

Signal reconstruction through software processing is a crucial component of the background and signal models in the PandaX-4T experiment, which is a multi-tonne dark matter direct search experiment. The accuracy of signal reconstruction is influenced by various detector artifacts, including noise, dark count of photomultiplier, photoionization of impurities in the detector, and other relevant considerations. In this study, we presented a detailed description of a semi-data-driven approach designed to simulate a signal waveform. This work provides a reliable model for the efficiency and bias of the signal reconstruction in the data analysis of PandaX-4T. By comparing critical variables that relate to the temporal shape and hit pattern of the signals, we found good agreement between the simulation and data.

Fast Coincidence Filter for Silicon Photomultiplier Dark Count Rate Rejection.

Silicon Photomultipliers find applications across various fields. One potential Silicon Photomultiplier application domain is neutrino telescopes, where they may enhance the angular resolution. However, the elevated dark count rate associated with Silicon Photomultipliers represents a significant challenge to their widespread utilization. To address this issue, it is proposed to use Silicon Photomultipliers and Photomultiplier Tubes together. The Photomultiplier Tube signals serve as a trigger to mitigate the dark count rate, thereby preventing undue saturation of the available bandwidth. This paper presents an investigation into a fast and resource-efficient method for filtering the Silicon Photomultiplier dark count rate. A low-resource and fast coincident filter has been developed, which removes the Silicon Photomultiplier dark count rate by using as a trigger the Photomultiplier Tube input signals. The architecture of the coincidence filter, together with the first results obtained, which validate the effectiveness of this method, is presented.

In-orbit dark count rate performance and radiation damage high-temperature annealing of silicon avalanche photodiode single-photon detectors of the Micius satellite.

Silicon avalanche photodiode (APD) single-photon detectors in space are continuously affected by radiation, which gradually degrades their dark count performance. From August 2016 to June 2023, we conducted approximately seven years (2507 days) of in-orbit monitoring of the dark count performance of APD single-photon detectors on the Micius Quantum Science Experimental Satellite. The results showed that due to radiation effects, the dark count growth rate was approximately 6.79 cps/day @ -24 °C and 0.37 cps/day @ -55 °C, with a significant suppression effect on radiation-induced dark counts at lower operating temperature. Based on the proposed radiation damage induced dark count annealing model, simulations were conducted for the in-orbit dark counts of the detector, the simulation results are consistent with in-orbit test data. In May 2022, four of these detectors underwent a cumulative 5.7 hours high-temperature annealing test at 76 °C, dark count rate shows no measurable changes, consistent with annealing model. As of now, these ten APD single-photon detectors on the Micius Quantum Science Experimental Satellite have been in operation for approximately 2507 days and are still functioning properly, providing valuable experience for the future long-term space applications of silicon APD single-photon detectors.

Fabrication and characterization of silicon SPADs with doping compensated avalanche region

The features of avalanche region are of importance of SPAD. An ideal broad and rectangular avalanche field may reduce dark count rate but could hardly be realized by actual fabricating technology. We propose a new fabrication process including successive boron and phosphorus diffusions for building special doping compensated avalanche region. A low dark count rate below 10 cps at −20 °C and high photon detection efficiency about 70% at 850 nm are achieved. The afterpulsing probabilities are 2.3% at 20 °C and 3% at 0 °C. FWHM of time resolution is 340ps.

SiPM understanding using simple Geiger-breakdown simulations

The results of a 1-D Monte-Carlo program, which simulates the avalanche multiplication in diodes with depths of the order of 1μm based on the method proposed in Ref.Windischhofer and Riegler (2023), are presented. The aim of the study is to achieve a deeper understanding of silicon photo-multipliers. It is found that for a given over-voltage, OV, the maximum of the discharge current is reached at the breakdown voltage, Ubd, and that the avalanche stops when the voltage drops to approximately Ubd−OV. This is completely different to the generally accepted understanding of SiPMs, that the discharge stops at about Ubd. Simulated characteristics of the avalanche breakdown, like the time dependence of the avalanche current, over-voltage dependence of the Geiger-breakdown probability and the gain for photons and dark counts, are presented and compared to experimental findings.

Room-temperature waveguide-coupled silicon single-photon avalanche diodes

Single photon detection is important for a wide range of low-light applications, including quantum information processing, spectroscopy, and light detection and ranging (LiDAR). A key challenge in these applications has been to integrate single-photon detection capability into photonic circuits for the realization of complex photonic microsystems. Short-wavelength (λ < 1.1 μm) integrated photonics platforms that use silicon (Si) as photodetectors offer the opportunity to achieve single-photon avalanche diodes (SPADs) that operate at or near room temperature. Here, we report the first waveguide-coupled Si SPAD. The device is monolithically integrated in a Si photonic platform and operates in the visible spectrum. The device exhibited a single photon detection efficiency of >6% for wavelengths of 488 and 532 nm with an excess voltage of <20% of the breakdown voltage. The dark count rate was below 100 kHz at room temperature, with the possibility of improving by approximately 35% by reducing the temperature to −5 °C.

Generalized time-bin quantum random number generator with uncharacterized devices

Random number generators (RNG) based on quantum mechanics are captivating due to their security and unpredictability compared to conventional generators, such as pseudo-random number generators and hardware-random number generators. This work analyzes evolutions in the extractable amount of randomness with increasing the Hilbert space dimension, state preparation subspace, or measurement subspace in a class of semi-device-independent quantum-RNG, where bounding the states’ overlap is the core assumption, built on the prepare-and-measure scheme. We further discuss the effect of these factors on the complexity and draw a conclusion on the optimal scenario. We investigate the generic case of time-bin encoding scheme, define various input (state preparation) and outcome (measurement) subspaces, and discuss the optimal scenarios to obtain maximum entropy. Several input designs were experimentally tested and analyzed for their conceivable outcome arrangements. We evaluated their performance by considering the device’s imperfections, particularly the after-pulsing effect and dark counts of the detectors. Finally, we demonstrate that this approach can boost the system entropy, resulting in more extractable randomness.

Design of the ASIC readout scheme for the JUNO-TAO experiment

The Taishan Antineutrino Observatory (TAO) has been proposed to precisely measure the reactor antineutrino spectrum with an energy resolution better than 2% at 1 MeV. It can provide a reference spectrum to the Jiangmen Underground Neutrino Observatory (JUNO) to enhance its sensitivity to the neutrino mass ordering measurement. In addition, TAO can also provide a benchmark to verify the nuclear database and conduct new physics searches. The TAO detector is a 2.8-ton liquid scintillator detector equipped with a 10 m2 silicon photomultiplier (SiPM) array to collect the light with a coverage of 94%. The TAO detector will be operated at -50 °C to suppress the SiPM dark count rate. In this work, we report on the design of a readout system based on the KLauS6 chip to handle the outputs from the SiPMs, which exhibits advantages of high granularity (potentially good particle identification) and large dynamic range. A dedicated mockup system has been built and its performance carefully evaluated both at room and low temperatures, measuring gain, charge linearity, signal-to-noise ratio, and dead time. The testing results show that the performance of this system can meet the requirements of TAO. However, an abnormal increase in current at 1.8 V analog power of the KLauS6 chip has been observed when operating it at temperatures below -20 °C, resulting in a potential risk on the long-term reliability. Therefore, the KLauS-based readout design is considered as an alternative option for the future upgrading of the TAO's readout system. This study also provides a reference and guidance for other relevant applications.

Enhancing stability of microchannel plates (MCPs) through freeze-drying method

The crystallization and gain decrease of microchannel plates (MCPs) have a significant impact on the dark noise and working life of optoelectronic devices. By employing a freeze-drying method instead of high-temperature drying during MCP manufacturing, stability can be improved. Freeze-drying at low temperatures (−100 °C) mitigates chemical reactions between potassium (K) and oxygen (O2) or water (H2O) in the secondary emission layer, reducing crystallization during production and storage. Furthermore, freeze-drying eliminates the need for organic solvents, which can lead to carbon (C) element pollution on the MCP surface. Minimizing C element pollution is beneficial in reducing unstable “gas gain” and attenuating MCP gain during electron scrubing. Long-term storage tests demonstrate that freeze-dried MCPs exhibit over 20% reduction in crystallization and more than 10% decrease in gain loss rates. These findings highlight freeze-drying as an effective approach to enhance MCP stability, resulting in photomultiplier tubes (PMTs) with lower dark counting rates and higher gains.

High-performance eight-channel system with fractal superconducting nanowire single-photon detectors

Superconducting nanowire single-photon detectors (SNSPDs) have become a mainstream photon-counting technology that has been used in various applications. So far, most multi-channel SNSPD systems, either reported in literature or been commercially available, are polarization sensitive, that is, the system detection efficiency (SDE) of each channel is dependent on the state of polarization of the to-be-detected photons. Here, we report on an eight-channel system with fractal superconducting nanowire single-photon detectors working in the wavelength range of 930-940 nm that all feature low polarization sensitivity. In a close-cycled Gifford-McMahon cryocooler system with the base temperature of 2.2 K, we install and compare the performance of two types of devices: (1) SNSPD, composed of a single, continuous nanowire, and (2) superconducting nanowire avalanche photodetector (SNAP), composed of 16 cascaded units of two nanowires electrically connected in parallel. The highest system detection efficiency (SDE) among the eight channels reaches 96−5+4%, with polarization sensitivity of 1.02 and dark-count rate of 13 counts per second. The average SDE for eight channels for all states of polarization is estimated to be 90 ± 5%. We conclude that both the SNSPDs and the SNAPs can reach saturated, high SDE at the wavelength of interest, and the SNSPDs show lower dark- (false-) count rates while the SNAPs show better properties in the time domain. Using this system, we showcase the measurements of the second-order photon-correlation functions of light emission from a single-photon source based on a semiconductor quantum dot and from a pulsed laser. We believe that our work provides new choices of systems with single-photon detectors combining the merits of high SDE, low polarization sensitivity, and low noise that can be tailored for different applications.

Room temperature operation of germanium-silicon single-photon avalanche diode.

The ability to detect single photons has led to the advancement of numerous research fields1-11. Although various types of single-photon detector have been developed12, because of two main factors-that is, (1) the need for operating at cryogenic temperature13,14 and (2) the incompatibility with complementary metal-oxide-semiconductor (CMOS)fabrication processes15,16-so far, to our knowledge, only Si-based single-photon avalanche diode (SPAD)17,18 has gained mainstream success and has been used in consumer electronics. With the growing demand to shift the operation wavelength from near-infrared to short-wavelength infrared (SWIR)for better safety and performance19-21, an alternative solution is required because Si has negligible optical absorption for wavelengths beyond 1 µm. Here we report a CMOS-compatible, high-performing germanium-silicon SPAD operated at room temperature, featuring a noise-equivalent power improvement over the previous Ge-based SPADs22-28 by 2-3.5 orders of magnitude. Key parameters such as dark count rate, single-photon detection probability at 1,310 nm, timing jitter, after-pulsing characteristic time and after-pulsing probability are, respectively, measured as 19 kHz µm-2, 12%, 188 ps, ~90 ns and <1%, with a low breakdown voltage of 10.26 V and a small excess bias of 0.75 V. Three-dimensional point-cloud images are captured with direct time-of-flight technique as proof of concept. This work paves the way towards using single-photon-sensitive SWIR sensors, imagers and photonic integrated circuits in everyday life.

Characterization of a Transmon Qubit in a 3D Cavity for Quantum Machine Learning and Photon Counting

In this paper, we report the use of a superconducting transmon qubit in a 3D cavity for quantum machine learning and photon counting applications. We first describe the realization and characterization of a transmon qubit coupled to a 3D resonator, providing a detailed description of the simulation framework and of the experimental measurement of important parameters, such as the dispersive shift and the qubit anharmonicity. We then report on a Quantum Machine Learning application implemented on a single-qubit device to fit the u-quark parton distribution function of the proton. In the final section of the manuscript, we present a new microwave photon detection scheme based on two qubits coupled to the same 3D resonator. This could in principle decrease the dark count rate, favoring applications like axion dark matter searches.

An efficient modeling workflow for high-performance nanowire single-photon avalanche detector

Single-photon detector (SPD), an essential building block of the quantum communication system, plays a fundamental role in developing next-generation quantum technologies. In this work, we propose an efficient modeling workflow of nanowire SPDs utilizing avalanche breakdown at reverse-biased conditions. The proposed workflow is explored to maximize computational efficiency and balance time-consuming drift-diffusion simulation with fast script-based post-processing. Without excessive computational effort, we could predict a suite of key device performance metrics, including breakdown voltage, dark/light avalanche built-up time, photon detection efficiency, dark count rate, and the deterministic part of timing jitter due to device structures. Implementing the proposed workflow onto a single InP nanowire and comparing it to the extensively studied planar devices and superconducting nanowire SPDs, we showed the great potential of nanowire avalanche SPD to outperform their planar counterparts and obtain as superior performance as superconducting nanowires, i.e. achieve a high photon detection efficiency of 70% with a dark count rate less than 20 Hz at non-cryogenic temperature. The proposed workflow is not limited to single-nanowire or nanowire-based device modeling and can be readily extended to more complicated two-/three dimensional structures.

Reduction of afterpulse and dark count effects on SPAD detectors using processing methods

Single-photon detector is a device that can detect fragile light signals such as photons. Noise is one of the major problems of Single-Photon Avalanche Diode (SPAD) in quantum communication and other applications. The two main noises in SPAD are afterpulse and dark count rate. Afterpulse is one of the most critical challenges of SPAD type InGaAs at 1550 nm wavelength. Several solutions have been presented to reduce noise. One of the most important methods presented is based on pulse gate. Pulse gate is effective in noise reduction by limiting SPAD operation time. Self-differentiating and up-conversion methods are also used in telecommunication wavelength SPADs to reduce noise, which have high implementation costs due to their complex structure. In this paper, we present a novel method for SPAD noise reduction. In this method, the time of SPAD output pulses is recorded and checked. The processor detects photon pulses and noise with a new algorithm. Noise pulses are removed, and photon pulses remain. This method is suitable for some Quantum Key Distribution (QKD) protocols that are simultaneous sender and receiver. It cannot be used in LiDAR and other similar asynchronous applications. The noise reduction method presented in this paper can be used for all types of single photon detectors and at different wavelengths. Also, this method can be used simultaneously with other noise reduction methods and it greatly reduces the amount of noise.