Supersized quantum sensors make faint photons easier to catch

Quantum sensors have become more advanced, enabling scientists to detect even the faintest photons with greater ease. These sensors, known as superconducting nanowire single-photon detectors (SNSPDs), work by utilizing superconductivity to detect individual photons. When a photon strikes the detector, it creates a tiny splash in the electric current, disrupting the superconductivity and generating a measurable electrical signal.

However, SNSPDs have some limitations. They typically require complex nanoscale fabrication techniques, and the edges of the superconducting detectors limit their performance. Fabrication defects also cap the maximum current flow. To overcome these challenges, researchers at the National Institute of Standards and Technology (NIST) decided to explore a larger approach.

In a recent study published in Optica, the NIST team found that scaling up the superconducting wires to one-tenth of a millimeter—more than 100 times wider than typical SNSPDs—could improve the detector's design and fabrication process. By increasing the wire's width, the team simplified the detector's structure and unlocked its true performance potential.

Traditionally, researchers focused on making smaller and smaller wires, which made fabrication increasingly difficult. However, the NIST researchers discovered that a wider wire allowed for better photon detection. When a photon hits the wider wire, it creates a larger hot spot, disrupting the superconductivity over a larger area. This results in a stronger voltage pulse, which can be easily detected by the readout electronics.

The wider SNSPDs are also polarization-insensitive, meaning they can detect photons regardless of the direction of their electric field. This improvement leads to more noticeable splashes when photons are detected, making it easier to read the signals.

The NIST researchers scaled up the wire to one-tenth of a millimeter in their study, and there is potential to go even wider. While it is unclear if wide SNSPDs can achieve the same 98% efficiency as their nanoscale counterparts, the team did achieve a significant milestone: their dark counts dropped by a billion times. This improvement in performance opens up new possibilities for various applications, such as healthcare imaging techniques and astronomy.