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A series superconducting nanowire single-photon detector is a high performance nanowire array detector that has the potential to reach a high system detection efficiency (SQE), a high counting rate (CR) and photon number resolving functionality. Interconnected with a simplified readout, it shows promise for large scale expansion and has good prospects for future applications in single-photon imaging, quantum optics, quantum computing and deep-space communication. In this paper, we demonstrate a high SQE and CR series superconducting nanowire single-photon detector with an active area of 20 × 20 μm2. The detector shows a maximum SQE of 68% at 1550 nm with a dark count rate of 200 Hz and a wide response wavelength from 1100–2000 nm. It also achieves a CR over 300 MHz at single photon power level and has the capability of resolving photon numbers by up to six photons.

Scientific Reports 6: Article number: 28095; published online: 14 June 2016; updated: 12 January 2017 The authors neglected to cite previous studies related to the use of current injection as a viable means to control SQUIDs. These additional references are listed below as references 1, 2 and 3 and should appear in the Introduction section as below.

We demonstrate a two-terminal single-photon detector array multiplexed using superconducting slow-wave transmission lines. The detector array is able to detect both photon arrival time and position, and can resolve up to two photons.

Many superconducting technologies such as rapid single flux quantum computing (RSFQ) and superconducting quantum interference devices (SQUIDs) rely on the modulation of nonlinear dynamics in Josephson junctions for functionality. More recently, however, superconducting devices have been developed based on the switching and thermal heating of nanowires for use in fields such as single photon detection and digital logic. In this paper, we use resistive shunting to control the nonlinear heating of a superconducting nanowire and compare the resulting dynamics to those observed in Josephson junctions. We show that interaction of the hotspot growth with the external shunt produces high frequency relaxation oscillations with similar behavior as observed in Josephson junctions due to their rapid time constants and ability to be modulated by a weak periodic signal. In particular, we use a microwave drive to pull and mix the oscillation frequency, resulting in phase locked features that resemble the AC Josephson effect. New nanowire devices based on these conclusions have promising applications in fields such as parametric amplification and frequency multiplexing.

We describe a superconducting three-terminal device that uses a simple geometric effect known as current crowding to sense the flow of current and actuate a readout signal. The device consists of a "Y"-shaped current combiner, with two currents (sense and bias) entering separately through the top arms of the "Y", intersecting, and then exiting together through the bottom leg of the "Y". When current is added to or removed from one of the arms (e.g., the sense arm), the superconducting critical current in the other arm (i.e., the bias arm) is modulated. The current in the sense arm can thus be determined by measuring the critical current of the bias arm, or inversely, the sense current can be used to modulate the state of the bias arm. The dependence of the bias critical current on the sense current occurs due to the geometric current crowding effect, which causes the sense current to interact locally with the bias arm. Measurement of the critical current in the bias arm does not break the superconducting state of the sense arm or of the bottom leg, and thus, quantized currents trapped in a superconducting loop were able to be repeatedly measured without changing the state of the loop. Current crowding is a universal effect in nanoscale superconductors, and so this device has potential for applicability across a broad range of superconducting technologies and materials. More generally, any technology in which geometrically induced flow crowding exists in the presence of a strong nonlinearity might make use of this type of device.

Integration with conventional electronics offers a straightforward and economical approach to upgrading existing superconducting technologies, such as scaling up superconducting detectors into large arrays and combining single flux quantum (SFQ) digital circuits with semiconductor logic gates and memories. However, direct output signals from superconducting devices (e.g., Josephson junctions) are usually not compatible with the input requirements of conventional devices (e.g., transistors). Here, we demonstrate the use of a single three-terminal superconducting-nanowire device, called the nanocryotron (nTron), as a digital comparator to combine SFQ circuits with mature semiconductor circuits such as complementary metal oxide semiconductor (CMOS) circuits. Since SFQ circuits can digitize output signals from general superconducting devices and CMOS circuits can interface existing CMOS-compatible electronics, our results demonstrate the feasibility of a general architecture that uses an nTron as an interface to realize a 'super-hybrid' system consisting of superconducting detectors, superconducting quantum electronics, CMOS logic gates and memories, and other conventional electronics., United States. Intelligence Advanced Research Projects Activity (W911NF-14-C0089), United States. Air Force. Office of Scientific Research (FA9550-14-1-0052)

We report on a method of nanoSQUID modulation which uses kinetic inductance rather than magnetic inductance to manip-ulate the internal fluxoid state. We produced modulation using injected current rather than an applied magnetic field. Using this injected current, we were able to observe the triangle-wave shaped modulation of the device critical current which was periodic according to the London fluxoid quantization condition. The measurement results also confirmed that the fluxoid state inside a superconducting loop can be manipulated using primarily kinetic inductance. By using primarily kinetic inductance rather than magnetic inductance, the size of the coupling inductor was reduced by a factor of 10. As a result, this approach may provide a means to reduce the size of SQUID-based superconducting electronics. Additionally, this method provides a convenient way to perform kinetic inductance characterizations of superconducting thin films., United States. Air Force Office of Scientific Research, National Science Foundation (U.S.) (NSF fellowship, iQuISE program, award number 0801525)

© 2018 Author(s). To analyze the switching dynamics and output performance of a superconducting nanowire single photon detector (SNSPD), the nanowire is usually modelled as an inductor in series with a time-varying resistor induced by the absorption of a photon. Our recent experimental results show that, due to the effect of kinetic inductance, for a SNSPD made of a nanowire of sufficient length, its geometrical length can be comparable to or even longer than the effective wavelength of frequencies contained in the output pulse. In other words, a superconducting nanowire can behave as a distributed transmission line so that the readout pulse depends on the photon detection location and the transmission line properties of the nanowire. Here, we develop a distributed model for a superconducting nanowire and apply it to simulate the output performance of a long nanowire designed into a coplanar waveguide. We compare this coplanar waveguide geometry to a conventional meander nanowire geometry. The simulation results agree well with our experimental observations. With this distributed model, we discuss the importance of microwave design of a nanowire and how impedance matching can affect the output pulse shape. We also discuss how the distributed model affects the growth and decay of the photon-triggered resistive hotspot.

Modeling of superconducting nanowire single-photon detectors typically requires custom simulations or finite-element analysis in one or two dimensions. Here, we demonstrate two simplified one-dimensional SPICE models of a superconducting nanowire that can quickly and efficiently describe the electrical characteristics of a superconducting nanowire. These models may be of particular use in understanding alternative architectures for nanowire detectors and readouts.

Polarization sensitive photo-detectors are the key to the implementation of the polarimetric imaging systems, which are proved to have superior performance than their traditional counterparts based on intensity discriminations. In this article, we report the demonstration of a superconducting nanowire single photon detector (SNSPD) of which the response is ultra-sensitive to the polarization state of the incident photons. Measurements carried out on a fabricated SNSPD show that a device efficiency of ~48% can be achieved at 1550 nm for the case of parallel polarization, which is ~420 times larger than that for the case of perpendicular polarization. While the reported polarization ultra-sensitive technique is demonstrated on a single-pixel SNSPD, it is also fully compatible with the multi-pixel SNSPD array platforms that emerged recently.

We report successful fabrication of niobium nitride single-photon detectors on aluminum nitride substrates. The fabricated detectors showed saturated detection efficiency at 2.45 K under 1550 nm illumination (indicating near-unity internal quantum efficiency), sub-60-ps jitter, and ∼6 ns reset time.

Over the past decade, superconducting nanowire single photon detectors (SNSPDs) have emerged as a key enabling technology for quantum optics and free-space optical communication. We review the operating principle and the latest advances in the performance of SNSPDs, such as extending sensitivity into the mid infrared, and the adoption of amorphous superconducting films. We discuss the limits and trade-offs of the SNSPD architecture and review novel device designs, such as parallel and series nanowire detectors (PNDs and SNDs), superconducting nanowire avalanche photodetector (SNAPs), and nanowire arrays with row-column readout, which have opened the pathway to larger active area, higher speed and photon-number resolution.

Detection jitter quantifies variance introduced by the detector in the determination of photon arrival time. It is a crucial performance parameter for systems using superconducting nanowire single photon detectors (SNSPDs). In this work, we have demonstrated that the detection timing jitter is limited in part by the spatial variation of the photon detection events along the length of the wire. We define this jitter source as a geometric jitter since it is related to the length and area of the SNSPD. To characterize the geometric jitter, we have constructed a differential cryogenic readout with less than 7 ps of an electronic jitter that can amplify the pulses generated from the two ends of an SNSPD. By differencing the measured arrival times of the two electrical pulses, we were able to partially cancel out the difference of the propagation times and thus reduce the uncertainty of the photon arrival time. We proved that the variation of the differential propagation time was a few ps for a 3 μm × 3 μm device, while it increased up to 50 ps for a 20 μm × 20 μm device. In a 20 μm × 20 μm large SNSPD, we achieved a 20% reduction in the overall detection timing jitter for detecting the telecom-wavelength photons by using the differential cryogenic readout., National Science Foundation (U.S.) (ECCS1-509486), United States. Air Force. Office of Scientific Research (ECCS1-509486), Roberto Rocca Foundation, Singapore. Agency for Science, Technology and Research (National Science Scholarship), United States. National Aeronautics and Space Administration (Space Technology Research Fellowship Grant NNX14AL48H)

This paper describes the construction of a cryostat and an optical system with a free-space coupling efficiency of 56.5% ± 3.4% to a superconducting nanowire single-photon detector (SNSPD) for infrared quantum communication and spectrum analysis. A 1K pot decreases the base temperature to T= 1.7 K from the 2.9 K reached by the cold head cooled by a pulse-tube cryocooler. The minimum spot size coupled to the detector chip was 6.6 ± 0.11 μm starting from a fiber source at wavelength, λ = 1.55 μm. We demonstrated photon counting on a detector with an 8 × 7.3 μm² area. We measured a dark count rate of 95 ± 3.35 kcps and a system detection efficiency of 1.64% ± 0.13%. We explain the key steps that are required to improve further the coupling efficiency., United States. Office of Naval Research (BAA 13-001), United States. Intelligence Advanced Research Projects Activity (FA8650-11-C7-105)

A novel device of tandem MQW EAMs monolithically integrated with a DFB laser is fabricated by an ultra-low-pressure (22 mbar) selective area growth MOCVD technique. Experimental results exhibit superior device characteristics with low threshold of 19 mA, output light power of 4.5 mW, and over 20 dB extinction ratio when coupled to a single mode fibre. Moreover, over 10 GHz modulation bandwidth is developed with a driving voltage of 2 V. Using this sinusoidal voltage driven integrated device, 10 GHz repetition rate pulse with an actual width of 13.7 ps without any compression elements is obtained.

Superconducting nanowire single photon detectors (SNSPDs) promise to combine near-unity quantum efficiency with >100 megacounts per second rates, picosecond timing jitter, and sensitivity ranging from x-ray to mid-infrared wavelengths. However, this promise is not yet fulfilled, as superior performance in all metrics is yet to be combined into one device. The highest single-pixel detection efficiency and the widest bias windows for saturated quantum efficiency have been achieved in SNSPDs based on amorphous materials, while the lowest timing jitter and highest counting rates were demonstrated in devices made from polycrystalline materials. Broadly speaking, the amorphous superconductors that have been used to make SNSPDs have higher resistivities and lower critical temperature (Tc) values than typical polycrystalline materials. Here, we demonstrate a method of preparing niobium nitride (NbN) that has lower-than-typical superconducting transition temperature and higher-than-typical resistivity. As we will ...

Nature Photonics 11, 247–251 (2017); published online 27 March 2017; corrected after print 14 August 2017. In the version of this Article originally published, in Fig. 3c, in the y axis label, the units '(c.p.s.)' should not have been included; the label should have read “Dark counts”. This has now been corrected in the online versions of the Article.

We designed, fabricated, and tested a one-dimensional array of superconducting-nanowire single-photon detectors, integrated with on-chip inductors and resistors. The architecture is suitable for monolithic integration on a single chip operated in a cryogenic environment, and inherits the characteristics of individual superconducting-nanowire single-photon detectors. We demonstrated a working array with four pixels showing position discrimination and a timing jitter of 124 ps. The electronic crosstalk between the pixels in the array was negligible.

A fiber-coupled superconducting nanowire single photon detector is presented considering practical applications. The system performances, such as dark count rate, system efficiency and noise equivalent power, are discussed. A system efficiency of 3% (1550 nm) and a dark count rate of 10 Hz at 4.2 K were achieved in experiment.

Niobium nitride superconducting nanowire single-photon detectors were fabricated on thermally oxidized silicon substrates with large active areas of 30 μm × 30 μm. To achieve non-constricted detectors, we improved the film growth and electron beam lithography process to fabricate uniform 100-nm wide NbN nanowires with a fill factor of 50%. The devices showed 72.4% system detection efficiency (SDE) at 100-Hz dark count rate (DCR) and 74-ps timing jitter, measured at the fiber communication wavelength of 1550 nm. The highest SDE which is 81.2% when the DCR is ~700 c/s appears at the wavelength of 1650 nm.

A novel device of tandem multiple quantum wells (MQWs) electroabsorption modulators (EAMs) monolithically integrated with DFB laser is fabricated by ultra-low-pressure (22 mbar) selective area growth (SAG) MOCVD technique. Experimental results exhibit superior device characteristics with low threshold of 19 mA, output light power of 4.5 mW, and over 20 dB extinction ratio when coupled into a single mode fiber. Moreover, over 10 GHz modulation bandwidth is developed with a driving voltage of 2 V. Using this sinusoidal voltage driven integrated device, 10GHz repetition rate pulse with a width of 13.7 ps without any compression elements is obtained.

Through the use of an impedance matched taper, be we demonstrate a reduction of the noise jitter in WSi SNSPDs to a level below the intrinsic effects, resulting in full-width at half-maximum values of 4.8 ps for 532 nm and 10.3 ps for 1550 nm single photons.

We developed waveguide integrated nanowire detectors, a distributed readout nanowire imager, and three-terminal electrical devices. The combination of these technologies promises a significant advance in the state of the art of nanowire superconducting detectors.