Supercooled platform for detecting single photons

Researchers from the University of Glasgow and STFC Rutherford Appleton Laboratory have developed a supercooled detector platform, capable of detecting single photons, which could find applications in cancer treatment, driverless cars and practical quantum communications.

Published as a letter in the journal Superconductor Science and Technology, the research builds on existing developments in extremely sensitive light sensors known as superconducting nanowire single-photon detectors (SNSPDs). SNSPDs are capable of detecting individual light quanta (photons) — even at infrared wavelengths.

While SNSPDs have facilitated numerous significant advances in quantum science over the last decade, they need to be cooled to just a few degrees above absolute zero (-273.15°C) in order to work effectively — a process which requires expensive and hazardous liquid helium, or a great deal of electrical power, to achieve. The research team has now developed a more portable, less power-hungry platform for SNSPDs, enabling it to be used outside of a laboratory environment for the first time.

“We’ve adapted technology initially developed for the European Space Agency’s Planck mission, which launched in 2009 and successfully surveyed cosmic background radiation in the microwave and infrared frequencies of the spectrum over four and a half years in space,” said Nathan Gemmell of the University of Glasgow, lead author of the paper.

“We’ve taken a fibre-optic coupled superconducting detector supplied by the Dutch start-up Single Quantum BV and housed it in a miniaturised cooler capable of reaching temperatures of 4.2 Kelvin, or -268.95°C, which runs from standard mains power.”

The University of Glasgow’s Professor Robert Hadfield, lead researcher on the project, said the researchers have “been able to use the SNSPD for infrared single-photon light detection and ranging, a form of distance measurement which could play a key role in the development of systems suitable for driverless cars in the future”.

“We’ve [also] been able to use the system to detect infrared photons at a wavelength of 1270 nm, the signature of a form of excited oxygen known as ‘singlet oxygen’, which plays a key role in many biological and physiological processes,” Professor Hadfield said.

“In a cancer treatment called photodynamic therapy (PDT), the treatment drug exchanges energy with surrounding oxygen molecules on optical excitation, creating singlet oxygen radicals which kill tumour cells.

“A miniaturised cooling platform like ours would make SNSPD use in clinical PDT much more practical, potentially making cancer treatments more effective.”

Superconductor Science and Technology editor-in-chief Dr Cathy Foley, from Australia’s own CSIRO, described the research as “very exciting” and “a genuine breakthrough”.

“This work shows that advances in cryogenic engineering will enable superconducting quantum technologies to have decisive impact in a host of real-world applications,” Dr Foley said.