NIST creates high-res single-photon superconducting camera

Researchers at the National Institute of Standards and Technology (NIST) have built a superconducting camera containing 400,000 pixels. The camera is made up of grids of ultrathin electrical wires, cooled to near absolute zero, in which current moves with no resistance until a wire is struck by a photon. In these superconducting-nanowire cameras, the energy imparted by a single photon can be detected because it shuts down the superconductivity at a particular location (pixel) on the grid. Combining all the locations and intensities of all the photons makes up an image.

Superconducting cameras allow scientists to capture weak light signals, from distant objects in space or parts of the human brain. Having more pixels could open up new applications in science or biomedical research. Creating a superconducting camera with a high number of pixels has posed a challenge because it would be all but impossible to connect every single chilled pixel among many thousands to its own readout wire. Each of the camera’s superconducting components must be cooled to ultralow temperatures to function properly, and individually connecting every pixel to the cooling system would be virtually impossible.

NIST researchers and their collaborators at NASA’s Jet Propulsion Laboratory, and the University of Colorado Boulder, overcame this obstacle by combining the signals from many pixels onto a few room-temperature readout wires. A general property of any superconducting wire is that it allows current to flow up to a certain maximum ‘critical’ current. The researchers applied a current just below the maximum to the sensors — under that condition, if a single photon strikes a pixel, it destroys the superconductivity and the current is no longer able to flow without resistance through the nanowire and is shunted to a resistive heating element connected to each pixel. The shunted current creates an electrical signal that can rapidly be detected.

The NIST camera is constructed to have intersecting arrays of superconducting nanowires that form multiple rows and columns. Each pixel — a tiny region centred on the point where individual vertical and horizontal nanowires cross — is defined by the row and column in which it lies. This arrangement allowed researchers to measure the signals coming from an entire row or column of pixels at a time rather than recording data from each individual pixel, thereby reducing the number of readout wires. The researchers placed a superconducting readout wire parallel to but not touching the rows of pixels and another wire parallel to but not touching the columns.

Once the new readout architecture had been developed, the researchers made rapid progress in increasing the number of pixels, from 20,000 to 400,000 pixels. The readout technology can be scaled up for even larger cameras, and a superconducting single-photon camera with tens or hundreds of millions of pixels could soon be available.

The researchers plan to improve the sensitivity of the prototype camera so that it can capture almost every single incoming photon. This will enable the camera to measure light in photon-based quantum computers and contribute to biomedical studies that use near-infrared light to analyse human tissue.

The research findings were published in the journal Nature.

Image credit: iStock.com/scyther5