'Nano-Kelvin' Thermometer Claimed World's Best

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The new thermometer forces red and green light to circulate thousands of times around the edge of a disc-shaped crystal.
School of Chemistry and Physics/University of Adelaide: James Anstie/IPAS

An Australian team of researchers have developed a thermometer that is several times more sensitive than the best produced so far.

If our body temperature is usually around 98.6 degrees Fahrenheit, then why do we feel really hot and uncomfortable when it's 98.6 degrees outside?
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The device, known as a 'nano-Kelvin thermometer', can measure temperature differences to 30 billionths of a degree, according to a report in the journal Physical Review Letters.

"It's three times better than the record," says author experimental physicist, Professor Andre Luiten of the University of Adelaide.

Thermometers must not only be as precise as possible, but they must selectively measure temperature change, rather than other changes in the environment.

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Luiten and colleagues have developed a new technique to do just this.

The technique involves forcing red and green light to circulate thousands of times around the edge of a disc-shaped crystal.

This resonating light is like sound in a "whispering gallery" - where you whisper near a curved wall and the sound races around the interior of the wall and you can hear it on the other side of the room.

"We're doing the exact same thing but with light racing around the disc," says Luiten.

The speed of the light in the crystal changes depending on the temperature of the disc.

"When we heat up our crystal in which the light is travelling, that changes the speed of light going around that crystal because the crystal is expanding," says Luiten.

By measuring the relative differences between the speed of the red and green light, the researchers can measure temperature changes within the disc to 30 billionths of a degree, compared to 100 billionth of a degree for previous light-based thermometers.

He says that the device is 30 times more precise than the best of the available lab temperature sensors.

Devices based on this technique could be used for other purposes, for example to sense changes in pressure or the concentrations of explosives or pollutants.

"Demonstrating very sensitive thermometers are like a stepping stone to this later phase."

As precise as it is, the system, like other precision temperature sensors cannot measure absolute temperature.

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"The system has no accuracy whatsoever," says Luiten. "It only senses changes in temperature."

"Our previous claim to fame was building very accurate clocks but these clocks can't tell you what time of the day it is either. They measure changes in the duration of time, such as the length of one second," he says.

But, he says in many industrial process the actual temperature doesn't really matter.

"What matters is that you can keep the temperature at a fixed value," says Luiten.

This article originally appeared on ABC Science Online.