1051-8223 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TASC.2018.2836989, IEEE Transactions on Applied Superconductivity Fr-C-DET-05 1 Abstract— Timing jitter inherent in photon detection by superconducting nanowire single-photon detectors has different values and behave differently for detection events originating in bends and in straights of nanowires. Generally, jitter is larger for events in bends. Although, for typical meandering nanowire, contribution of bends to the integral jitter is almost negligible due to small geometric weight of bends in the meander, it reduces the accuracy of extracting the value of local jitter in straights. Here we report on the intrinsic jitter, which was measured in a straight nanowire without bends. Standard deviation in the intrinsic jitter for detection events in the straight nanowire is smaller than 3.8 ps for photons with the wavelength 794 nm and 7.7 ps for 1560 nm. This value is less than jitter magnitudes in straights, which were extracted from the jitter measured previously for the meandering nanowire. Coupling of photons to the nanowire through sufficiently long optical fiber increases integral jitter and causes asymmetry in the jitter histogram. However, this optical asymmetry differs qualitatively from the asymmetry caused by the detection process itself at small photon energies. Key Words — timing jitter; superconducting nanowires; wire bends, dispersion jitter I. INTRODUCTION iming jitter in the arrival of the electric signal which manifests the event of photon detection is of crucial importance for many applications. For example, in tracking space debris [1] jitter restricts the accuracy of orbit reconstruction for midsize fragments. In time-of-flight laser ranging (LIDAR) [2, 3] jitter defines the depth resolution. For NbN superconducting nanowire single-photon detector (SNSPD), the FWHM (full width at half maximum) jitter as small as 22 ps was demonstrated [4]. However, in practical detection systems FWHM jitter typically amounts at several tens of picoseconds (See Ref. [5] and references therein). The reason is the large size of detectors which is required in order to achieve effective optical coupling between the detector area and a fiber. It has been shown that the duration of electrical This work was supported in part by The Helmholtz Research School on Security Technologies (HRSST) M. Sidorova and A. Semenov are with the Institute of Optical Systems of the German Aerospace Center (DLR), 12489 Berlin, Germany. (e-mail: Mariia.Sidorova@dlr.de). A. Kuzmin, S. Doerner, and M. Siegel are with the Institute of Micro- und Nanoelectronic Systems, Karlsruhe Institute of Technology (KIT), 76187 Karlsruhe, Germany (e-mail: artem.kuzmin@kit.edu). Ilya Charaev is with the Massachusetts Institute of Technology (MIT), Department of Electrical Engineering and Computer Science, Cambridge, MA 02139, USA (e-mail: charaev@mit.edu). pulses, which signal detection events, [6] and the timing-jitter in the arrival time of these pulses [7] both increase with the increase in the detector size. In Ref. 7 it was also reported that the arrival times of signal pulses originating from different locations in the nanowire are different. The increase in the pulse duration is readily explained by the kinetic inductance of the nanowire, which grows with the wire length, while the increase in the jitter may be the contribution of both the wire length and the detector geometry. The difference in the arrival times supports the idea that the nanowire in the detector can be treated as an electrical transmission line. Comparison of jitter in meanders with different nanowire-lengths but the same number of bends [8] has made it possible to separate contributions of bends and straights to the integral jitter. However, even small contribution of bends in meanders with large length of straights restricts the accuracy in defining the intrinsic jitter in straights. Moreover, in large meanders bends restrict measurable critical current and thus limit the range of currents in which jitter can be measured. Here we study jitter in straight nanowires without bends and compare it with the results obtained recently with meandering nanowires. II. EXPERIMENTAL APPROACH AND RESULTS Intrinsically timing jitter represents random variations in the time delay between photon absorption in the nanowire and the appearance of the voltage transient. Jitter measurements output the histogram of the delay time which is the probability density function (PDF) of the delay time considered as random continuous variable. PDF gives the density of probability for the delay time to have particular value. Additionally to the intrinsic jitter, measured jitter includes contributions due to variability of the flight-time of photons between the source and the wire (optical jitter) and due to electronic noise in the transient read-out. Furthermore, measured jitter is enhanced by the difference in traveling times of the voltage transients from different locations in the nanowire to input of the readout electronics (geometric jitter). Therefore, in order to minimize system contributions to the measured value, reliable method of measuring timing jitter requires high frequency and low noise electrical read-out as well as short-pulsed light source along with controllable optical coupling. We used room-temperature low noise amplifier (bandpass from 100MHz to 8GHz, noise figure 1.4 dB), sampling oscilloscope with a bandwidth of 50 GHz, DC current bias supplied by a battery-powered electronics, and sub-picosecond pulsed lasers. Samples, which are straight nanowires on sapphire substrates, were mounted Intrinsic Jitter in Photon Detection by Straight Superconducting Nanowires Mariia Sidorova, Alexej Semenov, Artem Kuzmin, Ilya Charaev, Steffen Doerner, M. Siegel T