Superconducting nanowire single photon detectors (SNSPDs) have the potential to function as highly accurate particle detectors, according to a study conducted at the U.S. Department of Energy’s Argonne National Laboratory. The findings could open new opportunities for the use of SNSPDs in the fields of nuclear and particle physics. SNSPDs are optical and IR photon sensors with precise spatial and timing resolutions. They are used to detect individual photons in quantum cryptography, optical sensing, and quantum computing applications. When SNSPDs absorb individual photons, small electrical changes in the nanowires are generated at very low temperatures, allowing the detection and measurement of single photons. The operating principles of SNSPDs suggest that they could function as precise particle sensors, especially for high-energy protons used as projectiles in particle accelerators. To investigate the potential of SNSPDs as particle detectors, the Argonne research team fabricated SNSPDs with different wire widths and tested the detectors with a beam of 120 gigaelectron volt (GeV) protons at a very low temperature of 2.82 Kelvins. The team conducted its experiments at the Test Beam Facility at the Department of Energy’s Fermi National Accelerator Laboratory (Fermilab). Close-up view of a superconducting nanowire single photon detector (SNSPD) mounted on a printed circuit board inside the cryostat at the Fermilab Test Beam Facility. This device was used in the first successful demonstration of high-energy proton detection using SNSPDs. Courtesy of Argonne National Laboratory/Sangbaek Lee. The sensors were fabricated out of 12 nm niobium nitride (NbN) thin film deposited by ion beam assisted sputtering on top of a 300 µm intrinsic silicon substrate. Thin films were patterned into nanowires using electron beam lithography, followed by inductively coupled plasma (ICP) reactive ion etching in a 20:25 mixture of CHF3:SF6 plasma. The researchers extracted the relative detection efficiency from bias current scans for each device. The results showed that wire width was a critical factor in determining the detection efficiency of the device. Wire widths larger than 400 nm led to inefficiencies at low bias currents. Wire widths smaller than 400 nm demonstrated the high detection efficiency required for high-energy proton sensing. The researchers determined that a wire size of approximately 250 nm was optimal for this application. “This was a first-of-its-kind use of the technology,” physicist Whitney Armstrong said. “This step was critical to demonstrate that the technology works the way we want it to because it is typically geared toward photons. It was a key demonstration for future high-impact applications.” In addition to providing sensitive, precise detection capabilities, SNSPDs are known to perform well under high magnetic fields, making them suitable for the superconducting magnets used in accelerators to boost particle velocity. “This was a successful technology transfer between quantum sciences, for photon detection, into experimental nuclear physics,” physicist Tomas Polakovic said. “We took the photon-sensing device and made slight changes to make it work better in magnetic fields and for particles. And behold, we saw the particles exactly as we expected.” The properties of SNSPDs align well with different particle detection applications and, when combined with low operating temperatures, could lead to new applications. For example, SNSPDs could be used in the Electron-Ion Collider (EIC)’s far-forward particle detection, which is an essential component of the EIC’s scientific mission. The EIC will collide electrons with protons and atomic nuclei to enable an investigation of the internal structure of the particles, including the quarks and gluons that comprise the protons and neutrons of nuclei. Reconstruction of these particles will require a detector with fast-timing, 100-µm pixel size. Geometrical acceptance of semiconductor detectors satisfying these requirements is limited by the beamline magnets. This could be mitigated by operating SNSPDs within the frigid bore of superconducting magnets. SNSPDs will be valuable tools for capturing and analyzing the particles produced in collisions within the EIC. “The proton energy range that we tested at Fermilab is right in the middle of the span of the ion’s energy range that we will detect at EIC, so these tests were well-suited,” physicist Sangbaek Lee said. The research was published in Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment (www.doi.org/10.1016/j.nima.2024.169956).
