Search

The practical application of Na-superionic conductor structured materials is hindered by limited energy density and structure damage upon activating the third Na

Quantum-inspired imaging techniques have been proven to be effective for LiDAR with the advances of single photon detectors and computational algorithms. However, the quantum-limited performance is still far from its ultimate limit set by the quantum fluctuations of signal and noise photons. In this work, we propose and demonstrate LiDAR from the detection perspective for approaching quantum-limited performance. A photon-number-resolving detector is introduced to accurately reconstruct the echo signals in a wide photon-flux range and an active photon number filter is further developed to overcome the heavy background noise. The Fisher information of this LiDAR based on a coherent source is only 0.04 dB below the quantum limit in intensity detection when mean signal photon number is 10. An improvement of 41.17 dB in the signal-to-background ratio is achieved with the proposed LiDAR in daytime, and the accuracy of intensity estimation is consistent with the theoretical prediction, which helps to improve the quality of reconstructed images. This work provides a fundamental strategy for constructing a noise tolerant LiDAR approaching quantum-limited precision.

Precisely acquiring the timing information of individual X-ray photons is important in both fundamental research and practical applications. The timing precision of commonly-used X-ray single-photon detectors remains in the range of one hundred picoseconds to microseconds. In this work, we report on high-timing-precision detection of single X-ray photons through the fast transition to the normal state from the superconductive state of superconducting nanowires. We successfully demonstrate a free-running X-ray single-photon detector with a timing resolution of 20.1 ps made of 100-nm-thick niobium nitride film with an active area of 50 μ m by 50 μ m. By using a repeated differential timing measurement on two adjacent X-ray single-photon detectors, we demonstrate a precision of 0.87 ps in the arrival-time difference of X-ray photon measurements. Therefore, our work significantly enhances the timing precision in X-ray photon counting, opening a new niche for ultrafast X-ray photonics and many associated applications.

The system detection efficiency of superconducting nanowire single-photon detectors ( SNSPD ) has rapidly improved in recent years. In this study, we fabricated NbN, WSi and MoSi ultra-thin films, which are widely used for SNSPD fabrication, employing magnetron sputtering. We characterized the films in the presence of a magnetic field to study the upper critical magnetic field Hc2 and the anisotropy. According to the results obtained in our experiments, we calculated the coherence length and diffusion coefficient of these films. The knowledge of these parameters will guide the modelling and the interpretation of the different features observed in SNSPD made out of NbN, WSi and MoSi.

Electrochemical energy storage has experienced unprecedented advancements in recent years and extensive discussions and reviews on the progress of multivalent metal-ion batteries have been made mainly from the aspect of electrode materials, but relatively little work comprehensively discusses and provides an outlook on the development of electrolytes in these systems. Under this circumstance, this Review will initially introduce different types of electrolytes in current multivalent metal-ion batteries and explain the basic ion conduction mechanisms, preparation methods, and pros and cons. On this basis, we will discuss in detail the research and development of electrolytes for multivalent metal-ion batteries in recent years, and finally, critical challenges and prospects for the application of electrolytes in multivalent metal-ion batteries will be put forward.

A superconducting nanowire single-photon imager (SNSPI) uses a time-multiplexing method to reduce the readout complexity. However, due to the serial connection, the nanowire should be uniform so that a common bias can set all segments of the nanowire to their maximum detection efficiency, which becomes more challenging as the scalability (i.e., the length of the nanowire) increases. Here, we have developed a 64-pixel SNSPI based on amorphous Mo

Many classic and quantum devices need to operate at cryogenic temperatures, demanding advanced cryogenic digital electronics for processing the input and output signals on a chip to extend their scalability and performance. Here, we report a superconducting binary encoder with ultralow power dissipation and ultracompact size. We introduce a multigate superconducting nanowire cryotron (nTron) that functions as an 8-input OR gate within a footprint of approximately 0.5 μm2. Four cryotrons compose a 4-bit encoder that has a bias margin of 18.9%, an operation speed greater than 250 MHz, an average switching jitter of 75 ps, and a power dissipation of less than 1 μW. We apply this encoder to read out a superconducting-nanowire single-photon detector array whose pixel location is digitized into a 4-bit binary address. The small size of the nanowire combined with the low power dissipation makes nTrons promising for future monolithic integration.

A fan-out circuit is a basic block for scaling up digital circuits for overcoming the limited driving capability of a single logic gate. It is particularly important for superconducting digital circuits as the driving power is typically weak for having high energy efficiency. Here, we design and fabricate a fan-out circuit for a superconducting nanowire cryotron (nTron) digital circuit. A classic splitter tree architecture is adopted. To transmit switching signal and avoid crosstalk among nTrons, we introduced an “R–L–R” interface circuit. Experimentally, a two-stage splitter tree of a fan-out number of four was demonstrated. Correct operation was observed with a minimum bit error rate (BER) of 10−6. The bias margin was 10% at BER of 10−4. The average time jitter was 82 ps. Moreover, crosstalk was not observed. Based on these results, we envision that the fan-out circuit can be used in future development of superconducting-nanowire-based circuits.

Designing a spectrometer without the need for wavelength multiplexing optics can effectively reduce the complexity and physical footprint. On the basis of the computational spectroscopic strategy and combining a broadband-responsive dynamic detector, we successfully demonstrate an optics-free single-detector spectrometer that maps the tunable quantum efficiency of a superconducting nanowire into a matrix to build a solvable mathematical equation. Such a spectrometer can realize a broadband spectral responsivity ranging from 660 to 1900 nm. The spectral resolution at the telecom is sub-10 nm, exceeding the energy resolving capacity of existing infrared single-photon detectors. Meanwhile, benefiting from the optics-free setup, precise time-of-flight measurements can be simultaneously achieved. We have demonstrated a spectral LiDAR with eight spectral channels. This spectrometer scheme paves the way for applying superconducting nanowire detectors in multifunctional spectroscopy and represents a conceptual advancement for on-chip spectroscopy and spectral imaging.

Direct time-domain sampling oscilloscopic capture of ultra-high bandwidth (32–102 GHz) modulated optical waveforms at 1550 nm is demonstrated at optical power levels below −100 dBm. To detect fast optical waveforms directly at power levels far below what traditional optical oscilloscope methods can measure, we use a time-correlated single-photon counting (TCSPC) sampling acquisition method, recently developed integrated electro-optic devices with >100 GHz electro-optic bandwidth, and single photon detectors with < 5 ps jitter. We show the reconstruction of the time domain signals by collecting histograms of time-binned single photons captured using TCSPC and characterize the spectral components in the frequency domain. The ability to acquire ultra-weak eye diagrams and identify high-frequency spectral components from a relatively small ensemble of single-photon measurements may lead to significant advances in optical waveform capture technology.

Superconducting series nanowire single-photon detectors (SNDs) have been used for resolving photon numbers. But it can also exhibit a higher counting rate than a single superconducting nanowire single-photon detector (SNSPD), because the serial architecture allows multiple detectors working in parallel and the inductance of each pixel is reduced. In this paper, we found each pixel of the SND could reset fast although the whole detector took a much longer time for recovering. Therefore, the speed of an SND with a large kinetic inductance of 1.25 μH was characterized and compared to a standard SNSPD with the same total inductance. By measuring the detected photon rate over the input photon rate, we obtained a photon counting rate enhancement by 7.5 times. Meanwhile, the timing jitter of the SND was 63 ps at single photon detection regime. Our results show that the series structure and the readout scheme are quite practical in realizing high speed single-photon detectors besides resolving photon numbers.

Photon-number-resolving (PNR) is an important functionality in many applications. The traditional single photon detectors (SNSPDs) operated with the conventional readout scheme does not have the PNR functionality. In this paper, we demonstrate a superconducting photon-number-resolving detector operating at the visible wavelength regime, based on the serial connection of six superconducting nanowires. The results of our 6-element PNR device show clear evidence of n -photons differentiation with n ranging from 1 to 6. The system detection efficiency reaches 54% with the dark counts rate below 10 Hz at 660 nm. The demonstrated 6-element PNR device does not require a complex readout circuit compared with the SNSPD array device, and is expected to have wider applications in addition to imaging and communication.

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.

Controlling thermal transport is important for a range of devices and technologies, from phase change memories to next-generation electronics. This is especially true in nano-scale devices where thermal transport is altered by the influence of surfaces and changes in dimensionality. In superconducting nanowire single-photon detectors, the thermal boundary conductance between the nanowire and the substrate it is fabricated on influences all of the performance metrics that make these detectors attractive for applications. This includes the maximum count rate, latency, jitter, and quantum efficiency. Despite its importance, the study of thermal boundary conductance in superconducting nanowire devices has not been done systematically, primarily due to the lack of a straightforward characterization method. Here, we show that simple electrical measurements can be used to estimate the thermal boundary conductance between nanowires and substrates and that these measurements agree with acoustic mismatch theory across a variety of substrates. Numerical simulations allow us to refine our understanding, however, open questions remain. This work should enable thermal engineering in superconducting nanowire electronics and cryogenic detectors for improved device performance.

A superconducting nanowire single-photon imager (SNSPI) uses a time-multiplexing method to reduce the readout complexity. However, due to the serial connection, the nanowire should be uniform so that a common bias can set all segments of the nanowire to their maximum detection efficiency, which becomes more challenging as the scalability (i.e., the length of the nanowire) increases. Here, we have developed a 64-pixel SNSPI based on amorphous Mo80Si20 film, which yielded a uniform nanowire and slow transmission line. Adjacent detectors were separated by delay lines, giving an imaging field of 270 µm × 240 µm. Benefiting from the high kinetic inductance of Mo80Si20 films, the delay line gave a phase velocity as low as 4.6 µm/ps. The positions of all pixels can be read out with a negligible electrical cross talk of 0.02% by using cryogenic amplifiers. The timing jitter was 100.8 ps. Saturated internal quantum efficiency was observed at a wavelength of 1550 nm. These results demonstrate that amorphous film is a promising material for achieving SNSPIs with large scalability and high efficiency.

We demonstrate a multilayer nanoscale cryogenic heater-based switch (M-hTron) that uses a normal-metal heater overlapping a thin-film superconductor separated by a thin insulating layer. The M-hTron eliminates leakage current found in three-terminal superconducting switches and applies heat locally to the superconductor, reducing the energy required to switch the device. Modeling using the energy-balance equations and the acoustic mismatch model demonstrates reasonable agreement with experiment. The M-hTron is a promising device for digital superconducting electronics that require high fan-out and offers the possibility of enhancing readout for superconducting-nanowire single-photon detectors.

The niobium nitride (NbN) nanowires fabricated with the high-quality ultra-thin NbN film with a thickness of 3 nm–6 nm were widely used for single photon detectors. These nanowires had a low aspect ratio, less than 1:20. However, increasing the thickness and the aspect ratio of highly-uniformed NbN nanowires without reducing the superconductivity is crucial for the device in detecting high-energy photons. In this paper, a high-quality superconducting nanowire with aspect ratio of 1:1 was fabricated with optimized process, which produced a superconducting critical current of 550 μA and a hysteresis of 36 μA at 2.2 K. With the optimization of the electron beam lithography process of AR-P6200.13 and the adjustion of the chamber pressure, the discharge power, as well as the auxiliary gas in the process of reactive ion etching (RIE), the meandered NbN nanowire structure with the minimum width of 80 nm, the duty cycle of 1:1 and the depth of 100 nm were finally obtained on the silicon nitride substrate. Simultaneously, the sidewall of nanowire was vertical and smooth, and the corresponding depth-width ratio was more than 1:1. The fabricated NbN nanowire will be applied to the detection of soft X-ray photon emitted from pulsars with a sub-10 ps time resolution.

Improvements in temporal resolution of single-photon detectors enable increased data rates and transmission distances for both classical and quantum optical communication systems, higher spatial resolution in laser ranging, and observation of shorter-lived fluorophores in biomedical imaging. In recent years, superconducting nanowire single-photon detectors (SNSPDs) have emerged as the most efficient time-resolving single-photon-counting detectors available in the near-infrared, but understanding of the fundamental limits of timing resolution in these devices has been limited due to a lack of investigations into the timescales involved in the detection process. We introduce an experimental technique to probe the detection latency in SNSPDs and show that the key to achieving low timing jitter is the use of materials with low latency. By using a specialized niobium nitride SNSPD we demonstrate that the system temporal resolution can be as good as 2.6 ± 0.2 ps for visible wavelengths and 4.3 ± 0.2 ps at 1,550 nm. Knowledge about detection latency provides a guideline to reduce the timing jitter of niobium nitride superconducting nanowire single-photon detectors. A timing jitter of 2.6 ps at visible wavelength and 4.3 ps at 1,550 nm is achieved.

Photon number resolving (PNR) is an important capacity for detectors working in quantum and classical applications. Although a conventional superconducting nanowire single-photon detector (SNSPD) is not a PNR detector, by arranging nanowires in a series array and multiplexing photons over space, such series PNR-SNSPD can gain quasi-PNR capacity. However, the accuracy and maximum resolved photon number are both limited by the signal-to-noise (SNR) ratio of the output pulses. Here, we introduce a matched filter, which is an optimal filter in terms of SNR for SNSPD pulses. Experimentally, compared to conventional readout using a room-temperature amplifier, the normalized spacing between pulse amplitudes from adjacent photon number detections increased by a maximum factor of 2.1 after the matched filter. Combining with a cryogenic amplifier to increase SNR further, such spacing increased by a maximum factor of 5.3. In contrast to a low pass filter, the matched filter gave better SNRs while maintaining good timing jitters. Minimum timing jitter of 55 ps was obtained experimentally. Our results suggest that the matched filter is a useful tool for improving the performance of the series PNR-SNSPD and the maximum resolved photon number can be expected to reach 65 or even large.

Terahertz (THz) photonic waveguides are of great importance in THz integrated technology, especially for versatile signal processing. However, in THz photonics, very few fundamental “building blocks” equivalent to those used in muti-functional electronics circuits exist. This study proposes a photonics-inspired micro-ring whispering gallery mode resonator (WGMR) waveguide with a standard waveguide-compatible package on silicon platform. A gradual taper is integrated on the same chip to improve the coupling efficiency and reduce transmission loss. The packaged WGMR waveguide with an operating range of 0.360 to 0.440 THz had a maximum measured extinction ratio of 32 dB at 0.390 THz, with a Q factor of 385 and an insertion loss of 2.6 dB. The compact and standard waveguide-compatible packaged WGMR can easily be integrated into practical terahertz application systems for THz signal processing and as a tool for the study of fundamental THz science.

Scalable superconducting nanowire single photon detector (SNSPDs) arrays require cryogenic digital circuits for multiplexing the output detection pulses. Among existing superconducting digital devices, superconducting nanowire cryotron (nTron) is a three-terminal device with an ultra-compact size, which is promising for large scale monolithic integration. In this report, in order to evaluate the potential and possibility of using nTrons for reading and digitizing SNSPD signals, we characterized the grey zone, speed, timing jitter and power dissipation of a proper designed nTron. With a DC bias on the gate, the nTron can be triggered by a few μA high and nanoseconds wide input signal, showing the nTron was capable of reading an SNSPD pulse at the same signal level. The timing jitter depended on the input signal level. For a 20 μA high and 5 ns wide input pulse, the timing jitter was 33.3 ps, while a typical SNSPD’s jitter was around 50 ps. With removing the serial inductors and operating it in an AC bias mode. The nTron was demonstrated to be operated at a clock frequency of 615.4 MHz, which was faster than the maximum counting rate of a typical SNSPD. In additional, with a 50 Ω bias resistor and biased at 17.6 μA, the nTron had a total power dissipation of 19.7 nW. Although RSFQ circuits are faster than nTrons, for reading SNSPD or other detector arrays that demands less operation speed, our results suggest a digital circuit made from nTrons could be another promising alternative.

Superconducting nanowire single photon detectors (SNSPDs) based on Si substrates have demonstrated excellent performance, such as high efficiency, low dark count rate, short reset time and low timing jitter. But due to the lattice mismatch between NbN and Si substrate, the performance of film is limited. To this end, Nb 5 N 6 layer is fabricated as the buffer layer between the NbN film and Si substrate, and that will reduce the mismatch and optimize superconducting properties of NbN films. The 6nm-thick film with a 65 nm-thick buffer layer shows the zero resistance critical temperature (Tc 0 ) of 13.27 K, which is 5 K higher than that without buffer. Based on the NbN film on the buffered substrate, we fabricated SNSPD devices demonstrate critical current $(\mathrm{I}_{\mathrm{C}})$ of $65 \mu \mathrm{A}$ which is $5 \sim 6$ times higher to the detectors without buffer. Besides, the experiment results prove that the buffer layer reduces the kinetic inductance, which fasten the recovery of nanowire.

Superconducting nanowire single-photon detectors (SNSPDs) wherein ultrathin films are fabricated on Si substrates are greatly affected by lattice mismatch between the thin film and the substrate. A buffer layer can be used to reduce such lattice mismatch or optimize the strain in the film, thereby improving device performance. We prepared and optimized Nb5N6 as a buffer layer and found that it considerably improved the properties of NbN films on Si substrates. The zero-resistance critical temperature (T C0) of a 3 nm thick NbN film with a 20 nm thick buffer layer was 10.3 K. SNSPDs with Nb5N6-buffered NbN films were fabricated and compared with normal devices; the fabricated devices had high hysteresis current and low timing jitter. Furthermore, we investigated the thermal diffusion process of the device based on the hysteresis current and hotspot relaxation time and found that Nb5N6 buffer layers enhance the thermal coupling between the superconducting film and substrates. The relaxation time of buffered SNSPD was 14.2 ps, which was shorter than that of nonbuffered SNSPD by 17.8 ps. These effects explain the performance improvement observed in the case of the buffered devices.

Amorphous materials are attractive candidates for fabricating the superconducting nanowire single-photon detectors (SNSPDs) due to their superior tolerance and scalability over crystalline niobium nitride. However, the reduced superconducting transition temperature degenerates both operating temperature and saturation efficiency. Herein, the SNSPD (6.5 nm thickness and 50 nm width) based on the amorphous Mo 0.8 Si 0.2 film with a high optical absorption coefficient demonstrates close-to-unity intrinsic detection efficiency for 1550 nm photons from 75 mK to 2.2 K. Further, a high-performance array SNSPD with optimized 90 nm-width wires is also demonstrated. As-fabricated uniform 4-pixel SNSPD exhibits a saturation plateau for the photon counts at 2.2 K, which overcomes the limitation of operation at low temperature ( < 1 K ) for traditional amorphous SNSPDs. Coupled with superior intrinsic quantum efficiency, highly efficient photon counts, and low dark count ratio, this detector paves a way for achieving high efficiency and superior yield for large array systems.

The quality of an image is limited to the signal-to-noise ratio of the output from sensors. As the background noise increases much more than the signal, which can be caused by either a huge attenuation of light pulses after a long-haul transmission or a blinding attack with a strong flood illumination, an imaging system stops working properly. Here we built a superconducting single-photon infrared camera of negligible dark counts and 60 ps timing resolution. Combining with an adaptive 3D slicing algorithm that gives each pixel an optimal temporal window to distinguish clustered signal photons from a uniformly distributed background, we successfully reconstructed 3D single-photon images at both a low signal level ( ∼ 1 average photon per pixel) and extremely high noise background (background-to-signal ratio = 200 within a period of 50 ns before denoising). Among all detection events, we were able to remove 99.45% of the noise photons while keeping the signal photon loss at 0.74%. This Letter is a direct outcome of quantum-inspired imaging that asks for a co-development of sensors and computational methods. We envision that the proposed methods can increase the working distance of a long-haul imaging system or defend it from blinding attacks.

We design and fabricate λ/2 coplanar waveguide NbN resonators, the thickness and length of which are only several nanometers and hundred microns, respectively. The quality factor of such compact resonators can reach up to 7.5 × 104 at single photon power level at 30 mK with the resonance frequency around 6.835 GHz. In order to tune the resonant frequency, the resonator is terminated to the ground with a dc-SQUID. By tuning the magnetic flux in the dc-SQUID, the effective inductance of the dc-SQUID is varied, which leads to the change in the resonant frequency of the resonator. The tunability range is more than 30 MHz and the quality factor is about 3 × 103. These compact and tunable NbN resonators have potential applications in the quantum information processing, such as in the precision measurement, coupling and/or reading out the quantum states of qubits.

Time-domain sampling oscilloscopic capture of ultra-high bandwidth modulated optical waveforms at 1550 nm is demonstrated at ultra-low power levels below −100dBm, with eye SNR varying from 13dB at 30 GHz to 6dB at 100 GHz.

Laser communication using photons should consider not only the transmission environment’s effects, but also the performance of the single-photon detector used and the photon number distribution. Photon communication based on the superconducting nanowire single-photon detector (SNSPD) is a new technology that addresses the current sensitivity limitations at the level of single photons in deep space communication. The communication’s bit error rate (BER) is limited by dark noise in the space environment and the photon number distribution with a traditional single-pixel SNSPD, which is unable to resolve the photon number distribution. In this work, an enhanced photon communication method was proposed based on the photon number resolving function of four-pixel array SNSPDs. A simulated picture transmission was carried out, and the error rate in this counting mode can be reduced by 2 orders of magnitude when compared with classical optical communication. However, in the communication mode using photon-enhanced counting, the four-pixel response amplitude for counting was found to restrain the communication rate, and this counting mode is extremely dependent on the incident light intensity through experiments, which limits the sensitivity and speed of the SNSPD array’s performance advantage. Therefore, a BER theoretical calculation model for laser communication was presented using the Bayesian estimation algorithm in order to analyze the selection of counting methods for information acquisition under different light intensities and to make better use of the SNSPD array’s high sensitivity and speed and thus to obtain a lower BER. The counting method and theoretical model proposed in this work refer to array SNSPDs in the deep space field.

In this study, three kinds of amendments including superphosphate, humic acid, and fly ash and their complex combination were adopted to passivate the artificially simulated Pb-and Cd-containing soils. The passivation efficiency evaluation was performed via the CaCl

A superconducting loop stores persistent current without any ohmic loss, making it an ideal platform for energy efficient memories. Conventional superconducting memories use an architecture based on Josephson junctions (JJs) and have demonstrated access times less than 10 ps and power dissipation as low as 10[superscript -19] J. However, their scalability has been slow to develop due to the challenges in reducing the dimensions of JJs and minimizing the area of the superconducting loops. In addition to the memory itself, complex readout circuits require additional JJs and inductors for coupling signals, increasing the overall area. Here, we have demonstrated a superconducting memory based solely on lithographic nanowires. The small dimensions of the nanowire ensure that the device can be fabricated in a dense area in multiple layers, while the high kinetic inductance makes the loop essentially independent of geometric inductance, allowing it to be scaled down without sacrificing performance. The memory is operated by a group of nanowire cryotrons patterned alongside the storage loop, enabling us to reduce the entire memory cell to 3 μm ×7 μm in our proof-of-concept device. In this work we present the operation principles of a superconducting nanowire memory (nMem) and characterize its bit error rate, speed, and power dissipation., United States. National Aeronautics and Space Administration (Research Fellowship Award NNX14AL48H), National Science Foundation (U.S.) Graduate Research Fellowship Program (Grant 1122374)

We present an optimized fabrication process for superconducting nanowire single-photon detectors that allowed us to obtain a yield of ~70% for detectors based on 80-nm-wide niobium nitride nanowires. We fabricated detectors that showed 24-ps timing jitter and saturated detection efficiency without the need for cryogenic amplifiers, allowing for operation in a low-bias low-dark-count-rate regime while operating at maximum detection efficiency., United States. Defense Advanced Research Projects Agency. Information in a Photon (InPho) Program (Grant W911NF-10-1-0416), United States. Army Research Office, National Science Foundation (U.S.) (Grant ECCS-1128222), United States. Air Force Office of Scientific Research (Grant FA9550-14-1-0052), Massachusetts Institute of Technology. Research Laboratory of Electronics (Claude E. Shannon Fellowship), National Science Foundation (U.S.). Interdisciplinary Quantum Information Science & Engineering (iQuiSE) Program (Grant 0801525), United States. Intelligence Advanced Research Projects Activity (Grant FA8650-11-C-7105), Chinese Scholarship Council (Grant 201161919021)

Conventional readout of a superconducting nanowire single-photon detector (SNSPD) sets an upper bound on the output voltage to be the product of the bias current and the load impedance, I B × Z load , where Z load is limited to 50 Ω in standard r.f. electronics. Here, we break this limit by interfacing the 50 Ω load and the SNSPD using an integrated superconducting transmission line taper. The taper is a transformer that effectively loads the SNSPD with high impedance without latching. At the expense of reduced maximum counting rate, it increases the amplitude of the detector output while preserving the fast rising edge. Using a taper with a starting width of 500 nm, we experimentally observed a 3.6× higher pulse amplitude, 3.7× faster slew rate, and 25.1 ps smaller timing jitter. The results match our numerical simulation, which incorporates both the hotspot dynamics in the SNSPD and the distributed nature in the transmission line taper. The taper studied here may become a useful tool to interface high-impedance superconducting nanowire devices to conventional low-impedance circuits., National Science Foundation (U.S.) (Contract ECCS-1509486)

Coincidence detection of single photons is crucial in numerous quantum technologies and usually requires multiple time-resolved single-photon detectors. However, the electronic readout becomes a major challenge when the measurement basis scales to large numbers of spatial modes. Here, we address this problem by introducing a two-terminal coincidence detector that enables scalable readout of an array of detector segments based on superconducting nanowire microstrip transmission line. Exploiting timing logic, we demonstrate a 16-element detector that resolves all 136 possible single-photon and two-photon coincidence events. We further explore the pulse shapes of the detector output and resolve up to four-photon coincidence events in a 4-element device, giving the detector photon-number-resolving capability. This new detector architecture and operating scheme will be particularly useful for multi-photon coincidence detection in large-scale photonic integrated circuits.