Query: superconducting nanowire single photon detector acceptance

title: Compact 1.7 K Cryocooler for Superconducting Nanowire Single Photon Detectors
abstract: State of the art superconductor based cryogenic detector systems are being installed at numerous research facilities worldwide and are achieving world record sensitivities in a variety of applications. Implementation has been greatly facilitated by closed cycle refrigeration. However, in many cases, cooling capacities of the refrigerators exceed requirements, at times by orders of magnitude, resulting in excessively large and cumbersome systems. The availability of more compact and lower power consumption systems should greatly facilitate further user acceptance. Toward this end, we are developing a compact 1.7 K closed cycle pulse tube/Joule Thomson hybrid cryocooler for superconducting nanowire single photon detectors. A laboratory prototype consisting of the pulse tube cooler and the Joule Thomson coldhead has demonstrated over 1.4 mW of cooling at 1.7 K. The Joule Thomson compressor is under development and remains the single largest risk item in terms of reliability. The system, designed for low manufacturing costs, is projected to consume on the order of 250 W total power, including power for cooling fans, thermometry, and detector electronics, and to be mountable within a standard equipment rack.  Applications for superconductor based sensors and electronics have been steadily increasing over the past several years in diverse areas such as astrophysics/cosmology,1 X ray spectroscopy,2 gamma ray spectroscopy,2 quantum information,3 and photon science.3 These systems operate at temperatures ranging from above 4 K to lower than 50 mK. Although these systems are developed by scientists with low temperature expertise, end users typically have minimal cryogenic experience, and therefore acceptance has been greatly facilitated by push button, closed cycle cryocoolers. The majority of these systems depend on precooling with commercial Gifford McMahon or valved pulse tube coolers, which were originally developed for applications requiring relatively large cooling capacities such as shield cooling in magnetic resonance imagers or cryopumping. As a result, for many, if not most of these systems, the size and power consumption of the system are orders of magnitude larger than necessary. For example, many transition edge sensor (TES) systems are cooled using adiabatic demagnetization refrigerators (ADRs) with cooling capacities of hundreds of nanowatts at temperatures below 100 mK. At the 4 K reject temperature for the ADR, the heat rejected is on the order of a milliwatt, yet precoolers with capacities on the order of a watt with a power draw of several kilowatts are used. Cryocoolers 20, edited by S.D. Miller, R.G. Ross, Jr. and J.R. Raab (c)PInternational Cryocooler Conference, Inc. Boulder, CO, 2018 295 While there are advantages for using excessively large coolers such as rapid cooldown be greatly enhanced by reducing their size and power. Such applications include secure quantum encrypted communication links3 that utilize superconducting nanowire single photon detectors (SNSPD) and superconducting transition edge sensor microcalorimeters for electron microscope microanalysis.2 Based on these considerations, we initiated the development of a compact cooler for an SNSPD detector system that will result in a form factor and low power draw of a standard rackmountable electronics instrument. The cooler is a pulse tube/Joule Thomson (PT/JT) hybrid, with the JT stage achieving 1.4 mW of cooling at 1.7 K, and the three stage pulse tube providing cooling at 80 K, 25 K, and 10 K. To date we have successfully developed the pulse tube cooler and JT coldhead, whereas the JT compressor and associated gas decontamination is still under development. We have previously published results on an early version of this cooler.4 In this paper we present that increased the cooling capacity at 10 K by 35 and reduced the minimum temperature from

title: Demonstration of sub 3 ps temporal resolution with a superconducting nanowire single photon detector
abstract: 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.

title: Scalable implementation of a superconducting nanowire single photon detector array with a superconducting digital signal processor.
abstract: A two dimensional single photon imaging system with high sensitivity and high time resolution is the ultimate camera and useful in a wide range of fields. A superconducting nanowire single photon detector (SSPD or SNSPD) is one of the best candidates for realizing such an ultimate camera due to its high detection efficiency in a wide spectral range, low dark count rate without after pulsing, and excellent time resolution. Here we propose a new readout scheme to realize a large scale imaging array based on SSPD, where a row column readout architecture is combined with a digital signal processor based on a single flux quantum (SFQ) circuit. A 16 pixel row column readout SSPD array is fabricated and measured with an SFQ digital signal processor. We successfully acquired spatial information as encoded digital bit codes with the temporal information of the photon detection. The system timing jitter was measured as <80 ps for all 16 pixels even through the SFQ signal processor, indicating the potential for an imaging array with an extremely high time resolution.

title: Single channel electronic readout of a multipixel superconducting nanowire single photon detector.
abstract: We present a time over threshold readout technique to count the number of activated pixels from an array of superconducting nanowire single photon detectors (SNSPDs) This technique places no additional heatload on the cryostat, and retains the intrinsic count rate of the time tagger. We demonstrate proof of principle operation with respect to a four pixel device. Furthermore, we show that, given some permissible error threshold, the number of pixels that can be reliably read out scales linearly with the intrinsic signal to noise ratio of the individual pixel response.

title: Waveguide Integrated Superconducting Nanowire Single Photon Detector Array for Ultra Fast Quantum Key Distribution
abstract: We present an array of 16 superconducting nanowire single photon detectors made from NbTiN thin films on Si3N4 waveguides that we interface with 3D printed couplers providing wide transmission bandwidth.

title: Superconducting Nanowire Single Photon Detector on Thin Film Lithium Niobate Photonic Waveguide
abstract: We integrate niobium nitride superconducting nanowire single photon detectors (SNSPDs) on thin film lithium niobate (LN) photonic waveguides. Further development of this technology may push towards more complex circuits and functionalities on this already promising platform.

title: Long Range Depth Imaging with 13ps Temporal Resolution using a Superconducting Nanowire Single Photon Detector
abstract: We demonstrate millimetre scale depth imaging up to 325 meters by deployment of a novel superconducting nanowire single photon detector with 13 ps FWHM instrument response function at 1550 nm wavelength.

title: Superconducting Nanowire Single Photon Detector Rise Time Analysis
abstract: We explore the limits of spatial, spectral, and photon number resolution in superconducting nanowire single photon detectors by characterizing the rising edge of a readout pulse with a low noise high bandwidth readout circuit.

title: Spatially Resolved Superconducting Nanowire Single Photon Detector Rise Time Analysis
abstract: We explore spatial and photon number resolution in superconducting nanowire single photon detectors through measurements of the rising edge of the readout pulse.

title: Origins of the wavelength dependent timing jitter in superconducting nanowire single photon detector
abstract: A 2D hot spot diffusion model for describing the superconducting nanowire response to single photon is presented. We develop the 1D hot belt model to 2D hot spot model and can capture the initial stage of the hot spot evolution after photon absorption, this is helpful to comprehensive understand the origins and underlying physics of time jitter in superconducting nanowire based single photon detectors. Furthermore, the developed model can qualitatively explain the asymmetry and photon wavelength dependent probability density function (PDF) of the delay time. We find that the left and right half of the PDF distributions respective exhibit the Gauss and non Gauss shape as increasing the excitation wavelength or decreasing the bias current, and the origins are discussed and analyzed in the framework of newly developed 2D model. The proposed 2D hot spot diffusion model will not only sheds light on the origin and influence of the timing jitter but will also reveal the work principle of the superconducting nanowire devices.