Single-photon imager based on a superconducting nanowire delay line

Journal name:
Nature Photonics
Year published:
Published online
Corrected online


Detecting spatial and temporal information of individual photons is critical to applications in spectroscopy, communication, biological imaging, astronomical observation and quantum-information processing. Here we demonstrate a scalable single-photon imager using a single continuous superconducting nanowire that is not only a single-photon detector but also functions as an efficient microwave delay line. In this context, photon-detection pulses are guided in the nanowire and enable the readout of the position and time of photon-absorption events from the arrival times of the detection pulses at the nanowire's two ends. Experimentally, we slowed down the velocity of pulse propagation to ∼2% of the speed of light in free space. In a 19.7 mm long nanowire that meandered across an area of 286 × 193 μm2, we were able to resolve ∼590 effective pixels with a temporal resolution of 50 ps (full width at half maximum). The nanowire imager presents a scalable approach for high-resolution photon imaging in space and time.

At a glance


  1. SNSPI.
    Figure 1: SNSPI.

    a, Architecture of the SNSPI. The nanowire transmission line (TL) and the impedance tapers were fabricated in coplanar-waveguide structures (the ground plane is not shown in the sketch). P1 and P2, detection pulses from the two ends. Amp., radiofrequency amplifier. b, A scanning electron micrograph of the top nine rows of the meandered nanowire (out of 15 rows in total). The dimensions shown are q = 13.0 μm, h = 9.7 μm and p = 5.4 μm. Inset scale bars, 2 μm (left) and 300 nm (right). c, A single-photon image of the pattern formed by light passing through a metal mesh, which was placed on top of the SNSPI with a gap of ∼200 μm (Supplementary Information gives the imaging set-up). The circular periodic patterns reflect the opening holes of the mesh. The wavelength of the light was 780 nm. The image consists of data from 427,905 photon-detection events. The colour of the map shows the normalized photon counts at each location. d, An optical micrograph of the metal mesh with an opening size of 43 μm and a wire diameter of 30 μm. Scale bar, 50 μm.

  2. Spatial and temporal detection by the SNSPI.
    Figure 2: Spatial and temporal detection by the SNSPI.

    a,b, Oscilloscope waveforms of output pulses from the two ends of the nanowire. We selected three pulse pairs whose arrival times corresponded to three different photon-detection locations. The device was illuminated with sub-picosecond optical pulses from a mode-locked laser at a wavelength of 1.5 μm. c, Histogram of 989,897 photon detections for imaging an array of institutional logos. The x axis is the position along the nanowire. A continuous-wave light-emitting diode source at 405 nm was used to project the object on the imager. The span of x was divided into 15 sections that correspond to the 15 rows (R1–R15) of the double-meandered nanowire. d, Image of one institutional logo constructed from the photon-position data (only a portion of the full image region is shown). e, Magnified section of the histogram that corresponds to the bright lines included within the green-shaded area in R6. f, Histogram of the difference between the photon-arrival time tp measured by the SNSPI and a reference time tr. We used a 1.5 μm mode-locked laser to illuminate the SNSPI and generate tr with picosecond resolution. The FWHM of the histogram profile was 50 ps, which was used to define the timing jitter jd.

  3. Detection performance of the SNSPI.
    Figure 3: Detection performance of the SNSPI.

    a, Photon count rate (PCR) versus IB at wavelengths from visible to infrared. The traces are normalized to the photon counts at 65 μA, where dark counts are 1 × 103 c.p.s., to limit the error in the measurement of net photon counts. The x axis is normalized to ISW (67.4 μA). b, Overall dark counts versus IB. c, Histogram of dark counts along the nanowire at IB = 65 μA. We selected the ten peaks with the highest amplitudes (indicated by the arrows above the peaks) and fit each of them with a Gaussian function, of which we then calculated the FWHM s. d, Distribution of s from the considered ten peaks, marked as the blue dots. The average of s is s̅ = 29.9 μm and the with s.d.(s) = 0.9 μm.

Change history

Corrected online 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.


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Author information


  1. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • Qing-Yuan Zhao,
    • Di Zhu,
    • Niccolò Calandri,
    • Andrew E. Dane,
    • Adam N. McCaughan,
    • Francesco Bellei,
    • Hao-Zhu Wang &
    • Karl K. Berggren
  2. Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milano 22020, Italy

    • Niccolò Calandri
  3. Department of Physics, University of North Florida, Jacksonville, Florida 32224, USA

    • Daniel F. Santavicca


Q.-Y.Z. and K.K.B. came up with the initial idea. Q.-Y.Z. designed and fabricated the nanowire imager. Q.-Y.Z. and D.Z. took the optical measurements. Q.-Y.Z., N.C., F.B. and H.-Z.W. characterized initial devices. A.E.D. developed the superconducting films. Q.-Y.Z., A.N.M. and D.F.S. did the microwave simulations. Q.-Y.Z. analysed the data and programmed the imaging script. K.K.B. supervised the project. Q.-Y.Z. and K.K.B. wrote the paper with input from all the other authors.

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