Superconducting cameras have long been hailed as powerful tools in capturing weak light signals for scientific and biomedical research. In a recent development, researchers at the National Institute of Standards and Technology (NIST) have successfully constructed a superconducting camera with 400,000 pixels, a significant increase from previous devices. This breakthrough has the potential to open up new applications and opportunities in various fields. The team’s findings were published in the October 26th edition of the scientific journal, Nature.
The NIST camera utilizes grids of ultrathin electrical wires that are cooled to near absolute zero. These wires operate in a superconducting state, where current flows without resistance until it is disrupted by the impact of a photon. By detecting the energy delivered by a single photon, the camera is capable of generating detailed images by combining all the locations and intensities of the photons. While the concept of superconducting cameras capable of sensing single photons was developed over two decades ago, previous devices were limited by the number of pixels they could accommodate.
One of the main challenges in increasing the pixel count of superconducting cameras is connecting each pixel to its own readout wire while maintaining the cooling system required for proper functioning. In order to overcome this obstacle, the NIST researchers, in collaboration with colleagues from NASA’s Jet Propulsion Laboratory and the University of Colorado Boulder, adopted a novel approach. Instead of individually connecting each chilled pixel to the readout wire, they combined the signals from multiple pixels onto just a few room-temperature wires.
The researchers took advantage of the property of superconducting wires to enable the flow of current up to a certain maximum, known as the “critical” current. By applying a current slightly below the maximum to the sensors, the team created a condition where a single photon striking a pixel would destroy the superconductivity and divert the current to a resistive heating element connected to that pixel. This shunted current then generates a detectable electrical signal, capturing the presence of the photon.
To increase the number of pixels without compromising the camera’s functionality, the NIST team developed an architecture with intersecting arrays of superconducting nanowires, resembling a tic-tac-toe grid. By defining each pixel based on its corresponding row and column, the team was able to measure the signals from entire rows or columns of pixels, significantly reducing the number of readout wires required. Two superconducting readout wires were positioned parallel to the rows and columns, respectively, and utilized to capture the signals.
When a photon strikes a pixel, the resulting shunted current in the resistive heating element generates a tiny hotspot in the parallel readout wire. This hotspot produces two voltage pulses, each traveling in opposite directions along the wire. Detectors at the ends of the wire record the arrival times of these voltage pulses, revealing the column in which the pixel resides. A similar mechanism is employed by the second readout wire, parallel to the columns. The detectors are highly sensitive, capable of discerning differences in signal arrival times as short as 50 trillionths of a second, and counting up to 100,000 photons striking the grid per second.
With the adoption of the new readout architecture, the NIST team saw rapid progress in increasing the number of pixels. In a matter of weeks, the pixel count jumped from 20,000 to an impressive 400,000 pixels. The researchers believe that the readout technology can be further scaled up to accommodate even larger cameras. In the near future, superconducting single-photon cameras with tens or hundreds of millions of pixels may become available.
Looking ahead, the NIST team plans to enhance the sensitivity of the prototype camera, enabling it to capture nearly every incoming photon. This improvement would enable the camera to undertake low-light imaging tasks, such as capturing images of faint galaxies or planets outside our solar system. Additionally, these cameras could contribute to the advancement of biomedical studies that utilize near-infrared light to examine human tissues. Furthermore, the technology could play a vital role in measuring light in photon-based quantum computers.
The development of a superconducting camera with 400,000 pixels brings new possibilities for scientific and biomedical research. The NIST team’s innovative approach in combining signals and minimizing the number of readout wires demonstrates a significant breakthrough in overcoming the limitations of previous devices. As the sensitivity and pixel count continue to evolve, the potential applications of superconducting cameras in capturing weak light signals will expand, opening new frontiers in various fields of study.