Quantum light makes better measurements

Scientists at Griffith University have made a breakthrough in measurement precision, achieving a result that has been a major goal of the scientific community for the last 30 years.

Published in Nature Photonics, researchers from Griffith University’s Centre of Quantum Dynamics have demonstrated that certain optical measurements using photons — or single particles of light — can be performed with a higher level of precision than could ever be achieved without quantum techniques.

“Over the centuries advancements in how precisely we can measure things have consistently resulted in new breakthroughs in science and technology. So, we hope our result will be important for the future,” said Professor Geoff Pryde, the team leader.

Theoretical physicists have predicted since the 1980s that certain pairs of light beams containing a specific number of photons can be used to extract the maximum amount of measurement information per particle. In this technique, the photons are entangled (or connected by quantum physics) between the two light beams. One beam interacts with the object being measured, and the other beam serves as a reference.

A big challenge is that these entangled quantum states are extremely sensitive to photons “going missing” when they are unintentionally absorbed or scattered in the measurement device.

Previous attempts by other scientists have had to ignore the missing photons, so that it was not possible for entangled photon states to beat ordinary light in a fair measurement comparison.

The Griffith University team used their recently-developed low-loss photon source in combination with high efficiency detectors–used in collaboration with the National Institute of Standards and Technology in the USA–to minimise the chance of photons going missing.

This allowed Pryde’s team to unconditionally demonstrate the advantage of using photon quantum measurement techniques to improve measurement precision, realising the promise of theory from decades ago.

Professor Pryde said a future goal of the photon research community would be to efficiently make and use bigger entangled states, which gives a bigger quantum advantage. Ultimately, the hope is that these quantum-enhanced measurements can be used to measure sensitive samples — such as quantum materials and biological systems — extracting the maximum information with the minimum damage to the sample.

“We want to see how far this technology can be pushed.”