Researchers at the National Institute of Standards and Technology (NIST) and colleagues have created a superconducting camera that contains 400,000 pixels, 400 times more than other devices of its kind. Superconducting cameras allow scientists to capture very weak light signals from distant objects in space or from parts of the human brain. More pixels could open the door to many new applications in science and biomedical research. The researchers reported their work in the publication Nature 26 October.

NIST’s chamber consists of grids of ultra-thin electrical wires cooled to near absolute zero, where current flows without resistance until a photon strikes the wire. In these superconducting nanowire cameras, the energy reported by even a single photon can be captured because they turn off superconductivity at a specific location (pixel) on the grid. The combination of all positions and intensities of all photons creates an image.

The first superconducting cameras capable of detecting single photons were developed more than 20 years ago. Since then, devices contain no more than a few thousand pixels; This is too limited for most applications.

The animation depicts a special reading system that allowed NIST researchers to create a single-photon camera composed of 400,000 superconducting nanowires, the highest-resolution camera of its kind. Further improvements would make the camera ideal for low-light tasks such as imaging faint galaxies or planets outside the solar system, measuring light in photon-based quantum computers, and biomedical research using near-infrared light to observe a person. cloth. Image credit: S. Kelly/NIST

Creating a superconducting camera with more pixels has become a major challenge; because it was almost impossible to connect each cooled pixel among thousands of pixels to its own reading cable. The problem lies in the fact that each of the superconducting camera components must be cooled to extremely low temperatures to function properly, and connecting each pixel out of millions of pixels individually to a cooling system would be nearly impossible.

NIST researchers Adam McCaughan and Bakhrom Oripov and their collaborators at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and the University of Colorado at Boulder overcame this obstacle by combining signals from many pixels over just a few wires to read room temperature.

The common property of any superconducting wire is that it allows current to flow freely up to a certain maximum “critical” current. To exploit this behavior, the researchers applied a current to the sensors just below the maximum value. In this case, even a single photon hitting a pixel would destroy superconductivity. Current can no longer flow unopposed through the nanowire and is instead directed to a small resistive heating element connected to each pixel. Shunt current creates an electrical signal that can be detected quickly.

Borrowing from existing technology, the NIST team built a chamber made of intersecting arrays of superconducting nanowires that formed multiple rows and columns like a game of tic-tac-toe. Each pixel, a small area centered at the intersection of individual vertical and horizontal nanowires, is uniquely identified by the row and column it is in.

This arrangement allowed the team to measure signals from an entire row or column of pixels simultaneously rather than recording data from each pixel, significantly reducing the number of readout wires. To do this, the researchers placed a superconducting readout wire in parallel but not touching the rows of pixels, and another wire in parallel but not touching the columns.

Consider a superconducting readout wire parallel to the banks only. When a photon hits a pixel, current directed to a resistive heating element heats a small section of the readout wire, creating a small hot spot. The hot spot produces two voltage pulses that travel in opposite directions along the readout cable and are recorded by detectors at both ends. The difference in the time it takes for pulses to reach the end detectors determines the column in which the pixel is located. A second superconducting readout wire running parallel to the columns performs a similar function.

Detectors can detect differences in arrival times of signals up to 50 trillionths of a second. They can also count up to 100,000 photons hitting the grating per second.

After the team adopted the new reading architecture, Oripov made rapid progress in increasing the number of pixels. Within a few weeks the number grew from 20,000 to 400,000 pixels. Mac Kogan said the readout technology could be easily scaled up for larger cameras, and a superconducting single-photon camera with tens or hundreds of millions of pixels could soon be available.

Over the next year, the team plans to improve the sensitivity of the prototype camera so that it can capture almost any incoming photon. This will allow the camera to perform low-light tasks such as imaging faint galaxies or planets beyond the solar system, measuring light in photon-based quantum computers, and aiding biomedical research that uses near-infrared light to look at a person’s tissue.