The 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,” project lead Professor Andre Luiten says.
“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 phenomena known as a “whispering gallery” – as seen in St Paul's Cathedral in London or the Whispering Wall at Barossa Reservoir – then we can measure this minuscule difference in speed with great precision.”
The technique could also be redesigned for ultra-sensitive measurements of other things such as pressure, humidity, force or searching for a particular chemical.
Professor Luiten says he believes it is the best measurement ever made of temperature – at room temperature. It is possible to make more sensitive measurements in low temperatures close to absolute zero.
“We’ve been able to measure temperature differences to 30 billionths of a degree in one second. To emphasise how precise this is, when we examine the temperature of an object we find that it is always fluctuating,” says 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 out thermometer, showing that the microscopic world is always in motion.”
“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,” Professor Luiten says.
The paper ‘Nano-Kelvin Thermometry and Temperature Control: Beyond the Thermal Noise Limit’ was published in the journal Physical Review Letters. PhD candidate Wenle Weng carried out the work.
Institute for Photonics and Advanced Sensing
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