"We have been able to measure temperature differences to 30 billionths of a degree in one second," said project leader Andre Luiten.

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," 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," he explained.

The new technique could be redesigned for ultra-sensitive measurements of other things such as pressure, humidity, force or searching for a particular chemical.

The findings were published in the journal Physical Review Letters.


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