Fermi National Accelerator Laboratory (Fermilab) scientists are leading a pair of photonics-related projects under the umbrella of the U.S. Department of Energy’s (DoE) Accelerate Innovations program. The initiatives aim to develop and extend the capabilities of existing superconducting nanowire single-photon detectors (SNSPDs), and enable large-scale particle sensors with 3D integrated circuits to process much smaller, much faster signals at a higher level of precision, respectively. The Fermilab projects are among 11 DoE national lab projects awarded a total of $73 million in funding over a two-year period. The funding aims to speed the transition of new technology from lab to industry. SNSPDs, the subject of the first project, are ultrafast light sensors that use a thin superconducting wire to detect single photons. Scientists operate them at very low temperatures and send an electric current through the wire just below the maximum that the material can withstand without turning normal conducting. When a single photon hits the nanowire, it transfers just enough energy to push the nanowire out of its superconducting state. This causes the material to develop electrical resistance, which creates a measurable voltage pulse. The SNSPD detectors under development at Fermilab will use very little energy and will be well-suited to detect faint photon signals formed by particle interactions which may indicate the existence of axions. The project aims to enable scientists to seek low-energy light from axions with masses in the mid-infrared range, equivalent to 0.05-1 eV. To date, this mass range has remained unexplored; no previous detection technology is sensitive enough to such low-energy signals. “Our project and funding are specifically for particle physics applications including dark matter searches,” said Fermilab’s Si Xie, principal investigator for the project. “But the result could have wide-ranging impact on diverse fields of science including the search for far away planets, environmental monitoring and climate change applications, and studying some biochemical processes.” Fermilab scientist Si Xie mounts a superconducting nanowire single photon detector inside a cryostat. He and his colleagues will use the detector to look for light created by dark matter particles. Courtesy of Fermilab/Christina Wang. To achieve their goal, the project team will construct and test prototype detectors with energy thresholds 20 or more times lower than that of conventional SNSPDs. Lower energy thresholds aid in efficient detection of low-frequency, low-energy photons in this range. As part of their work, the project team will develop specialized antenna structures. These will enable, for the first time, mid-IR SNSPD detectors with an active sensor area larger than 1 sq mm. They will also focus on improving the ultrafast signal readout by developing novel sensor electronics that extract and detect particle signals at greater resolution than existing SNSPDs. The second project, led by SLAC National Accelerator, seeks to enable large-scale particle sensors with 3D integrated circuits to process much smaller, much faster signals at a higher level of precision. Fermilab is a major collaborator, with Artur Apresyan and Davide Braga serving as co-investors. The sensors developed in the project will be part of 3D heterogeneously integrated detectors. The wafers are connected at the micrometer scale. This eliminates traditional larger interconnections and significantly improves the fidelity of signals all along the chain. “You can have a lower power because you are getting signals with low noise, so you can use resources more optimally and you can do a lot more with those resources,” Apresyan said. While the current generation of this technology uses rather large pixels of approximately 1 mm, the goal is to scale this down to 50-µm pixels. “We want to demonstrate 3D integrated sensors that utilize low gain avalanche detector particle sensors that provide very fast timing information,” said Braga. “We intend to simultaneously achieve 10-micron position resolution and 10-picosecond precision timing while consuming low power and reaching high throughput rates.” The team is also partnering with a commercial chip company to develop advanced manufacturing capability for this novel technology. Their fabrication know-how will be essential for the co-design of sensor and electronics for scaling, Braga said.
