World's most sensitive thermometer created

Researchers from the Institute for Photonics and Advanced Sensing (IPAS) at the University of Adelaide have produced what is claimed to be the world’s most sensitive thermometer. The new and unorthodox method uses light to measure temperature.

“We believe this is the best measurement ever made of temperature - at room temperature,” said project leader Professor Andre Luiten, who noted that it is possible to make more sensitive measurements of temperature in cryogenic environments near absolute zero.

Writing in the journal Physical Review Letters, the researchers describe how their thermometer injects two colours of light (red and green) into a highly polished crystalline disk. The two colours travel at slightly different speeds in the crystal, depending on the temperature of the crystal.

“When we heat up the crystal, we find that the red light slows down by a tiny amount with respect to the green light,” Professor Luiten said.

“By forcing the light to circulate thousands of times around the edge of this disk in the same way that sound concentrates and reinforces itself in a curve in a phenomenon known as a ‘whispering gallery’ … then we can measure this minuscule difference in speed with great precision.”

The researchers report they have been able to measure temperature with a precision of 30 billionths of a degree in one second. That makes their thermometer three times more precise than the best thermometers in existence.

“To emphasise how precise this is, when we examine the temperature of an object we find that it is always fluctuating,” said Professor Luiten. “We all knew that if you looked closely enough you find that all the atoms in any material are always jiggling about, but we actually see this unceasing fluctuation with our thermometer, showing that the microscopic world is always in motion.”

Professor Luiten believes the technique could be redesigned for ultrasensitive measurements of other things such as pressure, humidity, force or searching for a particular chemical.

“Being able to measure many different aspects of our environment with such a high degree of precision, using instruments small enough to carry around, has the capacity to revolutionise technologies used for a variety of industrial and medical applications where detection of trace amounts has great importance,” he said.