A team of Australian scientists has produced a precision laser device that creates an accurate international standard for temperature.
Published today in the journal Nature Communications, the researchers from the University of Adelaide, University of Queensland and University of Western Australia have come up with a new way to determine Boltzmann’s constant, a number which relates the temperature of a system to its energy.
The experiments contribute to a worldwide scientific effort in redefining the international unit of temperature: the kelvin (zero kelvin or ‘absolute zero’ is the absence of all thermal energy and equivalent to -273.15 degrees celsius).
University of Adelaide’s Institute for Photonics and Advanced Sensing Director and project leader Professor Andre Luiten said the researchers used lasers to make highly accurate measurements of the speed of individual atoms moving in a gas.
“Although temperature is a familiar concept to all of us, remarkably it can only be measured accurately at a handful of locations around the globe,” he said.
“An atom sitting at rest will absorb light of a particular frequency or colour ─ if it is moving towards you or away from you then the absorbed light is very slightly changed because of something called the Doppler effect.
“This is exactly the same effect that makes a police siren sound different depending on whether the car is moving towards you or away. We use a pure laser to measure these changes in light absorption, from which we can infer the speeds of the atoms and the temperature of the gas.”
By conducting the experiments with world-record precision the team came across a completely unexpected effect. The light has an apparent effect on the atoms themselves: the measurement itself ends up changing the result. One of the breakthroughs of the project was to develop an explanation of how this happened and ensuring that it didn't affect the result.
ARC Centre for Engineered Quantum Systems and University of Queensland Associate Professor Tom Stace said the development meant any laboratory in the world could accurately measure temperature without needing sensitive calibration.
“Traditionally scientists kept a set of special clocks, rulers and standard masses to define units such as the second, metre and kilogram,” said Associate Professor Stace.
“Over the last 50 years we have been getting rid of these standards and replacing them with references that are based on universal quantities such as the speed of light or the frequency at which certain atoms vibrate.
“This program is completed for time and length, but mass and temperature still make use of special objects. In the case of temperature, it is based on the freezing point of a very special type of water to define the kelvin which makes it difficult for all laboratories around the world to agree about temperature.
“Our work will bring a universally agreed temperature scale to the globe. As with any upgrade, this one will be deemed successful if people hardly notice the transition on a day-to-day basis.
“But for those at the cutting edge -- whether developing new metal alloys at very high temperatures, or measuring the temperatures of the coldest substances, the need for absolute temperature is critical.”
Further development could deliver this capability to industry – something never before possible. "One of our next steps is to develop industry partnerships to apply our technique to very precise materials processing applications.”
Media: Associate Professor Tom Stace, stace@physics.uq.edu.au, +61 7 3365 1868 or +61 404 413 069
