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Demonstration of sub-3 ps temporal resolution with a superconducting nanowire single-photon detector


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.

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Fig. 1: Wavelength and bias current dependence of intrinsic detection latency and jitter as well as the effect of electrical noise jitter.
Fig. 2: Low-jitter SNSPD.
Fig. 3: Bias current dependence of the jitter, normalized PCR and relative detection latency.
Fig. 4: Wavelength dependence of the jitter.
Fig. 5: Few-photon scanning laser-ranging with sub-millimetre depth resolution.

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Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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Part of the research was performed at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). Support for this work was provided in part by the Defense Advanced Research Projects Agency, Defense Sciences Office, through the Detect programme and the National Science Foundation under grant number ECCS-1509486. E.A.B., A.E.D., G.M.C. and J.P.A. acknowledge partial support from the NASA Space Technology Research Fellowship programme. E.R. acknowledges support from the MARC-U*STAR programme. D.Z. acknowledges support from the A*STAR National Science Scholarship. M.S., S.X. and C.P. acknowledge partial and N.S. full support from the Alliance for Quantum Technologies’ (AQT) Intelligent Quantum Networks and Technologies (INQNET) research programme. M.S., C.P. and S.X. acknowledge partial support from the Department of Energy, High Energy Physics QuantISED programme grant, QCCFP (Quantum Communication Channels for Fundamental Physics), award number DE-SC0019219. C.P. acknowledges partial support from the Fermilab’s Lederman Fellowship. We thank P. Day, B. Putnam, D. Santavicca, J. Breffke, W. Becker and W. Rippard for valuable discussions and loan of measurement equipment as well as JPL and Caltech staff for technical support. The use of trade names is intended to allow the measurements to be appropriately interpreted and does not imply endorsement by the US government, nor does it imply these are necessarily the best available for the purpose used here.

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Authors and Affiliations



B.K. and Q.-Y.Z. conceived and designed the experiments. B.K., Q.-Y.Z., S.F., J.P.A., E.R., E.A.B., M.J.S., T.M.A., G.M., M.C., C.P., N.S., A.E.V., V.B.V., S.X., D.Z. and A.E.D. performed the experiments. B.K., S.F. and J.P.A. analysed the data. J.P.A. carried out the simulations. B.K., Q.-Y.Z., S.F., E.A.B., T.G., M.J.S., T.M.A., G.M., M.C., A.D.B., B.B., R.M.B., C.P., N.S., A.E.L., A.E.V., V.B.V., S.X., D.Z., A.E.D., E.E.W., G.M.C., J.P.A., J.D.R., P.D.H., K.L.S., R.P.M., M.S., S.W.N., F.M., A.G.K., M.D.S. and K.K.B. contributed materials/analysis tools. B.K., Q.-Y.Z., J.P.A. and M.D.S. wrote the paper with input from all authors.

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Correspondence to Boris Korzh.

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Extended data

Extended Data Fig. 1 Temperature dependence of the jitter.

a,b, Jitter (a) and normalized photon count rate (b) as a function of bias current for the 80 nm-wide nanowire measured with 1550 nm light at different operating temperatures between 0.9 K and 4 K. At 4 K, a shift of about 5 ps in the timing jitter was measured in the 11–13 µA range. The switching current drops below 14 µA at 4 K due to the elevated temperature, making jitter measurements above this current impossible at this temperature. It was independently verified that the shape of the electrical pulse and the level of the amplifier noise were independent of the operating temperature. The presence of this reduction in the timing jitter at higher temperatures is an indication that the intrinsic jitter mechanism is being observed.

Extended Data Fig. 2 Experimental setup for relative latency and jitter characterization.

To investigate the photon energy dependence of jitter and detection latency, we used a 0.5 mm-long, periodically poled lithium niobate (PPLN) second harmonic generation (SHG) crystal to frequency double a 1550 nm mode-locked laser (0.5 ps nominal pulse width) to 775 nm. After the crystal, the light was collimated and free-space coupled into the cryostat through a series of glass windows in the vacuum chamber and the heat shields at 40 K and 4 K, flood illuminating the device under test. The polarization of the light was orientated parallel to the nanowire (TE polarization). The optical intensity was controlled with a circular, metallic variable neutral-density filter. This configuration ensured that the converted 775 nm light and the unconverted 1550 nm light co-propagated via the same path through the optical setup. It was calculated that the 775 nm pulse was delayed by 1.1 ± 0.1 ps, relative to the 1550 nm light, due to chromatic dispersion in the optical elements after the SHG crystal. All detection latency results presented in this work have been corrected for this offset. After generation, filters were used to select the 1550 nm or 775 nm wavelength illumination. A synchronization signal was generated by splitting a fraction of the 1550 nm pump light with a fibre coupler and sending it onto a fast photodetector. We verified that the SNSPDs were operating in the single-photon detection regime by characterizing the detection rate as a function of incident optical power at different bias currents and operating in the range yielding linear dependence.

Extended Data Fig. 3 Relative latency and jitter measurements with WSi.

a, The PCR curves and b, corresponding relative latency between 775 nm and 1550 nm light detections for a 160 nm-wide WSi detector with the same design as the NbN detectors. The film thickness was 3.5 nm giving a critical temperature of 3.4 K and a room temperature sheet resistance of 422 Ω□-1. The depairing current (Idep) was estimated to be 14.1 μA by fabricating resonator devices, just as for NbN devices. A switching current of about 11.5 μA was achieved with the low jitter device, which is >0.8Idep. This means that the WSi and NbN devices are similar in terms of uniformity, since they achieve similar fractions of the depairing current. The relative latency increases from 12 ps to 80 ps when decreasing bias current from 0.78Idep to 0.43Idep, while the 120 nm-wide NbN device resulted in approximately 6 ps and 23 ps at comparable fractions of the depairing current. Due to the larger intrinsic latency in the WSi device, the resulting jitter is also larger as illustrated in c. At a bias current of 11.0 μA the jitter is 7.7 ps and 16.2 ps for 775 nm and 1550 nm light, respectively, while for the 120 nm NbN device the corresponding jitter is 4.5 ps (775 nm) and 7.7 ps (1550 nm) at the same fraction of the depairing current.

Extended Data Fig. 4 Slew rate independence on illumination wavelength.

SNSPD signal rising edge slope as a function of bias current for the 100 nm nanowire. Data for the 775 nm and 1550 nm illuminations show that the pulse signal pulse shape is independent of photon energy. The slope changes with bias current because the signal amplitude increases with the bias current flowing in the SNSPD.

Extended Data Fig. 5 Few-photon laser ranging demonstration.

Table-top few-photon laser ranging setup based on a 1064 nm mode-locked laser and a low jitter SNSPD. The scanner used coaxial alignment of the transmit and return beam, using a circulator based on a polarizing beam splitter and a quarter wave-plate.

Extended Data Fig. 6 Time of arrival histograms with a translating mirror.

By replacing the target with a translating mirror a, shows the resulting instrument response function fit with the mirror at different positions, demonstrating that an accurate time of arrival can be extracted. The full system jitter was 6.2 ps. The mirror position was swept and the laser pulse return time was extracted by using either the first b, 1000 detected photons or c, 20 detected photons. Using fewer photons increases the position uncertainty, however, millimetre accuracy is still possible even with 20 detected photons.

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Supplementary Notes 1–3, Figs. 1–4 and Table 1.

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Korzh, B., Zhao, QY., Allmaras, J.P. et al. Demonstration of sub-3 ps temporal resolution with a superconducting nanowire single-photon detector. Nat. Photonics 14, 250–255 (2020).

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