Ultrafast readout circuit enables 100 million-pixel superconducting nanowire detector

Superconducting nanowires have been used for decades as detectors for photons, neutrons, and other energetic particles. When a particle interacts with the nanowire, it creates a hotspot, briefly raising the temperature of the wire above the superconducting threshold and triggering a voltage pulse.

This detection method can even be used to build a functioning camera sensor by overlapping two meandering nanowires in a grid pattern. This setup, called the current-biased kinetic inductance detector (CB-KID), can identify the originating position of a particle by timing the difference between voltage pulses at each end of the nanowire. In this case, the resolution of the sensor is determined by the speed of the readout circuit.

Ishida et al. developed a high-speed readout circuit featuring a continuous readout data acquisition system and a high-resolution time-to-digital converter with a temporal resolution of 30 ps. This gives their 15 mm square sensor a pixel size of 1.5 µm, for 100 million total pixels.

This approach is necessary for superconducting detectors due to the cryogenic temperatures involved.

“Conventional imaging devices require a dedicated sensor and readout circuit for each pixel of a large-pixel image,” said author Takekazu Ishida. “Attempting to apply this to superconducting imaging elements is hindered by heat flow from room temperature. Our method requires only four readout lines, even for very large pixels.”

The authors have previously tested their sensor on neutrons produced by nuclear reactions; however, their wide spread limits the spatial resolution the detector can obtain.

“Moving forward, we plan to conduct experiments using a laser to inject photons into the CB-KID,” said Ishida. “This approach has the potential to demonstrate a spatial resolution equivalent to the pixel size.”

Source: “400-milion-pixel superconducting delay-line camera with 30-ps readout circuit,” by Takekazu Ishida, Hiroaki Shishido, The Dang Vu, Kenji M Kojima, and Tomio Koyama, AIP Advances (2025). The article can be accessed at https://doi.org/10.1063/5.0292145 .