A new technique that uses quantum light to measure temperature at the nanoscale

Being able to measure and monitor temperatures and temperature changes at tiny scales – inside a cell or in micro and nanoelectronic components – can impact many research areas ranging from From disease detection to a major challenge of modern computing and communication technologies, how to measure the scalability and performance of electronic components.

A collaborative team, led by scientists at the University of Technology Sydney (UTS), has developed an extremely sensitive nano-thermometer that uses atom-like inclusions in diamond nanoparticles to accurately measure temperature at the nanoscale. The sensor exploits the properties of these diamond-like diamond inclusions at the quantum level, where the limits of classical physics no longer apply.

Diamond nanoparticles are extremely small particles, up to 10,000 times smaller than the width of a human hair, which become fluorescent when they are laser-lit.

Dr. Carlo Bradac, Senior Researcher at the Faculty of Mathematics and Physical Sciences at UTS, said the new technique was not just a "proof of concept achievement".

"The method is immediately deployable, and we are currently using it to measure temperature changes in biological samples and in high-power electronic circuits that rely heavily on monitoring and controlling their temperature with sensitivities and a high degree of accuracy. Scale hard to reach with other methods, "said Dr. Bradac.

The study published in Progress of science, is a collaboration between UTS researchers and international collaborators from the Russian Academy of Sciences (UK), Nanyang Technological University (SG) and Harvard University (USA).

The main author, the UTS physicist, Dr. Trong Toan Tran, explained that, although pure diamond is transparent, it "usually contains imperfections such as foreign atom inclusions" .

"In addition to giving diamond different colors, yellow, pink, blue, etc., imperfections emit light at specific wavelengths [colours] when probed with a laser beam, "says Dr. Tran.

The researchers discovered that there was a special diet, called Anti-Stokes, in which the intensity of the light emitted by these diamond-colored impurities very strongly depended on the temperature of the environment. Because these diamond nanoparticles can be as small as a few nanometers, they can be used as tiny nano-thermometers.

"We immediately realized that we could exploit this particular fluorescence-temperature dependence and use diamond nanoparticles as ultra-small temperature probes," said Dr. Bradac.

"This is particularly interesting because the diamond is considered non-toxic – so it is suitable for measurement in delicate biological environments – but also extremely resistant – so it is ideal for measuring temperatures in very harsh environments up to several times. hundreds of degrees, "he added.

Researchers say that an important advantage of the technique is that it is all optical. The measurement only requires placing a droplet of the nanoparticle solution in the water in contact with the sample, and then measuring – non-invasively – their optical fluorescence when a laser beam is projected onto them.

Although similar all-optical approaches using nanoparticles have made it possible to measure temperatures at the nanoscale, the research team believes that none of them has been in the past. able to achieve both the sensitivity and the spatial resolution of the technique developed at UTS. "We believe that our sensor can measure temperatures with a sensitivity comparable to or better than the current best all-optical micro-and nano-thermometers, while offering the highest spatial resolution to date," said Dr. Tran.

UTS researchers pointed out that nanoscale thermometry was the most obvious – but far from the only – application of the Anti-Stokes regime in quantum systems. This regime can serve as a basis for exploring fundamental interactions between light and matter in isolated quantum systems at energies not explored conventionally. It opens up new possibilities for a multitude of practical nanoscale detection technologies, some as exotic as optical refrigeration where light is used to cool objects.