New quantum sensing method for greenhouse gas detection

A University of Bristol physicist has proposed an innovative technique to detect and characterise molecules with greater precision, paving the way for advances in environmental monitoring, medical diagnostics and industrial processes. The new quantum sensing method builds on the work of 2005 Nobel laureates in physics John Hall and Theodor Hänsch, who developed a frequency comb technique to accurately measure optical frequencies. Frequency combs are used in many areas of science and industry to characterise matter based on the unique way light is absorbed.

However, the precision of optical comb spectroscopy is limited by a fundamental level of noise present in all lasers and other classical sources of light. A quantum state with reduced noise called ‘squeezed light’ can overcome this limitation and has been harnessed to improve the sensitivity of gravitational wave detectors. In a paper published in Physical Review Letters, squeezed light is shown to suppress noise over a broad set of comb frequencies used to probe an absorbing molecule.

Author Alex Belsley, quantum engineering PhD student, said the research proposes a new method for monitoring gas species in situ and with high precision. “Quantum advantage in sensing can be realised today and I’m excited for the transformative impact quantum-enhanced sensors will have on our society in the coming years,” Belsley said.

This approach could potentially achieve a significant improvement in detection limits. In addition to allowing different types of gases to be characterised at ultra-low concentrations, it can also determine properties such as temperature and pressure with high sensitivity. Professor Jonathan Matthews, Belsley’s PhD advisor, said better sensors are important to our future, as health care, manufacturing, environmental monitoring and new science can all benefit from advances in how physical properties are measured.

“Alex’s work shows how squeezed light can improve frequency comb spectroscopy — the next step is to explore further with experiments in the lab,” Matthews said.

Image caption: Illustration of an optical frequency comb probing gas molecules. Image credit: Alex Belsley