Superconducting Nanowire Single-photon Detector System Research Articles

Superconducting nanowire single photon detector under AC-bias with self-differential readout

Superconducting nanowire single photon detector (SNSPD) has been widely used in many fields such as quantum computing, quantum key distribution and laser radar, due to its high detection efficiency, low dark count rate, high counting rate, and low timing jitter. In most cases, the SNSPD works under the DC-bias mode that can detect single photons arrived at any time. In some cases such as satellite laser ranging and single-photon laser radar where the light pulses arrive regularly, the AC-bias mode enables the SNSPD to work with higher counting rates and lower background dark counts, which however requires complicated readout due to the low signal-to-noise ratio of the photon response. In this work, we report on an AC-biased SNSPD system with a self-differential readout circuit. The system includes a 2-pixel SNSPD consisting of two parallel nanowires, which are biased with 100 MHz sinusoidal current. The output signals of these two nanowires are amplified and combined for the differential readout of the photon response. The resulting response pulse possesses a signal-to-noise ratio ten times higher than that extracted before self-differential readout. In addition, the dark counts are reduced by a factor of 4, and the count rates are increased by a factor of 1.5, in comparison with those under the DC-bias mode. This work provides a specific method to read out the AC-biased SNSPD.

Pulse-gated mode of commercial superconducting nanowire single photon detectors* *Project supported by the National Natural Science Foundation of China (Grant No. 61605248) and the National Basic Research Program of China (Grant No. 2013CB338002).

High detection efficiency and low intrinsic dark count rate are two advantages of superconducting nanowire single photon detectors (SNSPDs). However, the stray photons penetrated into the fiber would cause the extrinsic dark count rate, owing to the free running mode of SNSPDs. In order to improve the performance of SNSPDs in realistic scenarios, stray photons should be investigated and suppression methods should be adopted. In this study, we demonstrate the pulse-gated mode, with 500 kHz gating frequency, of a commercial SNSPD system for suppressing the response of stray photons about three orders of magnitude than its free-running counterpart on the extreme test conditions. When we push the gating frequency to 8 MHz, the dark count rate still keeps under 4% of free-running mode. In experiments, the intrinsic dark count rate is also suppressed to 4.56 × 10−2 counts per second with system detection efficiency of 76.4372%. Furthermore, the time-correlated single-photon counting analysis also approves the validity of our mode in suppressing the responses of stray photons.

Suppressing Dark Counts of Multimode-Fiber-Coupled Superconducting Nanowire Single-Photon Detector

Large active-area superconducting nanowire single-photon detectors (SNSPDs) coupled with multimode fibers (MMFs) can provide high light-gathering capacity, which is essential for free-space detection applications in photon-starved regimes. However, MMF-coupled SNSPDs often suffer from large system dark count rates (DCRsys) over kHz due to blackbody radiation of the MMF at room temperature. Such large DCRsys would significantly degrade signal-to-noise ratio (SNR) of the receiving system. This paper reports an MMF-coupled large-active-area SNSPD system with low DCRsys by using a homemade cryogenic MMF filter bench. The filter bench, which consists of lenses and optical filters, can provide a high transmittance of about 80% at the central wavelength of the passband (1550±12.5 nm) and a wide blocking range from 500 nm to over 6000 nm at 40 K. With using the filter bench, the DCRsys of an MMF-coupled 9-pixel SNSPD array with an active area of 50 μm in diameter is greatly suppressed by 23 dB with 1 dB loss of system detection efficiency (SDE). The detector demonstrates an SDE of 51% at a DCRsys of 100 Hz for 1550 nm photons. Thus, SNR of the detector is enhanced by about 160 times and the noise equivalent power is improved to 3×10 $^{-19}$ W/Hz $^{1/2}$ .

Single-Flux-Quantum Based Event-Driven Encoder for Large-Pixel Superconducting Nanowire Single-Photon Detector Array

We propose a single-flux-quantum (SFQ) based event-driven encoder for a large-pixel superconducting nanowire single-photon detector (SSPD) array with a row-column readout architecture. The designed SFQ encoder can acquire time-tagged address data with a high time resolution. To apply 32 × 32 pixel SSPD system with a row-column architecture, the SFQ encoder is equipped with two 32-channel input ports among which one is for positive pulses, whereas the other is for negative pulses. The number of Josephson junctions (JJs) in the designed circuit is 2780. The power dissipation and required total bias current are 0.21 mW and 170 mA, respectively, owing to the reductions in critical currents of the JJs and bias resistors. The circuit generates time-tagged address data by applying electrical pulses at room temperature not only in liquid helium but also in a 0.1-W Gifford-McMahon (GM) cryocooler.

Scalable cryogenic readout circuit for a superconducting nanowire single-photon detector system.

The superconducting nanowire single-photon detector (SNSPD) is a leading technology for quantum information science applications using photons, and is finding increasing uses in photon-starved classical imaging applications. Critical detector characteristics, such as timing resolution (jitter), reset time, and maximum count rate, are heavily influenced by the readout electronics that sense and amplify the photon detection signal. We describe a readout circuit for SNSPDs using commercial off-the-shelf amplifiers operating at cryogenic temperatures. Our design demonstrates a 35 ps timing resolution and a maximum count rate of over 2 × 107 counts per second, while maintaining <3 mW power consumption per channel, making it suitable for a multichannel readout.

Superconducting nanowire single photon detection system for space applications.

Superconducting nanowire single photon detectors (SNSPDs) have advanced various frontier scientific and technological fields such as quantum key distribution and deep space communications. However, limited by available cooling technology, all past experimental demonstrations have had ground-based applications. In this work, we demonstrate a SNSPD system using a hybrid cryocooler that could ultimately be compatible with space applications. With a minimum operational temperature of 2.8 K, this SNSPD system presents a maximum system detection efficiency of over 50% and a timing jitter of 48 ps, which paves the way for various space applications.

Improving the timing jitter of a superconducting nanowire single-photon detection system

Low timing jitter is a unique merit of superconducting nanowire single-photon detectors (SNSPDs) for time-correlated applications. Quantitative analysis was performed for the SNSPD system. Aided by an oscilloscope with an optimal signal amplitude, we were able to measure a full width at half-maximum system timing jitter as low as 14.2 ps for a high-switching-current SNSPD using a room-temperature low-noise amplifier. When using a time-correlated single-photon counting module, the system timing jitter was 17.3 ps. The detector's intrinsic timing jitter was estimated at ∼12.0 ps.

Bias-free true random number generation using superconducting nanowire single-photon detectors

We demonstrate a bias-free true random number generator (TRNG) based on single photon detection using superconducting nanowire single photon detectors (SNSPDs). By comparing the photon detection signals of two consecutive laser pulses and extracting the random bits by the von Neumann correction method, we achieved a random number generation efficiency of 25% (a generation rate of 3.75 Mbit s−1 at a system clock rate of 15 MHz). Using a multi-channel superconducting nanowire single photon detector system with controllable pulse signal amplitudes, we detected the single photons with photon number resolution and positional sensitivity, which could further increase the random number generation efficiency. In a three-channel SNSPD system, the random number bit generation efficiency was improved to 75%, corresponding to a generation rate of 7.5 Mbit s−1 with a 10 MHz system clock rate. All of the generated random numbers successfully passed the statistical test suite.

Review of superconducting nanowire single-photon detector system design options and demonstrated performance

We describe a number of methods that have been pursued to develop superconducting nanowire single-photon detectors (SNSPDs) with attractive overall performance, including three systems that operate with >70% system detection efficiency and high maximum counting rates at wavelengths near 1550 nm. The advantages and tradeoffs of various approaches to efficient optical coupling, electrical readout, and SNSPD design are described and contrasted. Optical interfaces to the detectors have been based on fiber coupling, either directly to the detector or through the substrate, using both single-mode and multimode fibers with different approaches to alignment. Recent advances in electrical interfaces have focused on the challenges of scalability and ensuring stable detector operation at high count rates. Prospects for further advances in these and other methods are also described, which may enable larger arrays and higher-performance SNSPD systems in the future. Finally, the use of some of these techniques to develop fully packaged SNSPD systems will be described and the performance available from these recently developed systems will be reviewed.

超伝導ナノワイヤ単一光子検出器

We present our recent progress in development of a superconducting nanowire single-photon detector (SSPD) system. Our practical SSPD system with a compactGifford-McMahon cryocooler successfully achieved the high system detection efficiency of 74%, low dark count of 100 cps, and small timing jitter of 68 ps in one device simultaneously, which is useful for actual applications. Furthermore, we propose and demonstrate a new strategy to resolve a trade-off problem between the system detection efficiency and counting rate (speed) in the SSPD.

High-speed and high-efficiency superconducting nanowire single photon detector array

Superconducting nanowire single photon detectors (SNSPDs) have separately demonstrated high efficiency, low noise, and extremely high speed when detecting single photons. However, achieving all of these simultaneously has been limited by detector subtleties and tradeoffs. Here, we report an SNSPD system with <80 ps timing resolution, kHz noise count rates, and 76% fiber-coupled system detection efficiency in the low-flux limit at 1550 nm. We present a model for determining the detection efficiency penalty due to the detection recovery time, and we validate our method using experimental data obtained at high count rates. We demonstrate improved performance tradeoffs, such as 68% system detection efficiency, including losses due to detector recovery time, when coupled to a Poisson source emitting 100 million photons per second. Our system can provide limited photon number resolution, continuous cryogen-free operation, and scalability to future imaging and GHz-count-rate applications.

Single photon response of superconducting nanowire single photon detector

Single photon detection is one of the key technologies for quantum key distribution in quantum communication. As a novel single photon detection technology, superconducting nanowire single photon detector (SNSPD) surpasses conventional semiconducting single photon detectors with high count rate and low dark count rate. In this article, we introduce SNSPD fabricated from NbN ultrathin superconducting film and lab-based SNSPD system. The characteristics of single photon response pulse of SNSPD are analyzed in detail. Also discussed is the relationship between waveform of single photon response and system bandwidth. Circuit model is made to analyze the performance of SNSPD. The simulation result agrees well with the experimental data. Those results are valuable for understanding the mechanism of SNSPD and building future SNSPD system for quantum communication.

Development of SNSPD System With Gifford-McMahon Cryocooler

A superconducting nanowire single photon detector (SNSPD) system for telecommunication wavelength using a GM cryocooler was developed and its performance was verified. The cryocooler based SNSPD system can operate continuously with a 100 V AC power supply without any cryogen. The packaged SNSPD device was cooled to 2.96 K within a thermal fluctuation range of 10 mK. An SNSPD with an area of 20 times 20 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> showed good system detection efficiency (DE) at 100 Hz dark count rate of 2.6% and 4.5% at wavelengths of 1550 and 1310 nm, respectively. An SNSPD with an area of 10 times 10 mum <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and kinetic inductance lower than that of the large area device showed good system DE of 2.6% at a wavelength of 1550 nm. The SNSPD system could be operated for over 10 h with constant system DE and dark count rate.