Theoretical physicists from Trinity College Dublin (TCD) have helped create an engine completely invisible to the naked eye. As part of an international collaboration, they have revealed what amounts to the world’s smallest engine made from a single calcium ion.

This makes it approximately 10bn times smaller than a car engine and could be used in technologies to recycle waste heat with the goal of improving energy efficiency. Writing in Physical Review Letters, the researchers said that the engine is electrically charged, making it easy to trap in electric fields.

The working substance of the engine is the ion’s ‘intrinsic spin’, which is used to convert heat absorbed from laser beams into vibrations of the trapped ion.

In effect, these vibrations act as a ‘flywheel’ capturing the useful energy produced by this tiny engine. Once generated, it is stored in discrete units called ‘quanta’, as predicted by the laws of quantum mechanics.

‘Ushers in a new era’
Dr Mark Mitchison, one of the article’s co-authors and a member of the college’s QuSys group, said: “The flywheel allows us to actually measure the power output of an atomic-scale motor, resolving single quanta of energy, for the first time.”

When starting the flywheel from ‘ground state’ – the lowest energy state in quantum physics – the researchers noted that the engine forced the flywheel to run faster and faster. Importantly for their research, the state of the ion was accessible during the experiment, allowing the physicists to precisely assess the energy deposition process.

TCD’s John Goold said this experiment and theory “ushers in a new era for the investigation of the energetics of technologies based on quantum theory”.

“Heat management at the nanoscale is one of the fundamental bottlenecks for faster and more efficient computing,” he said. “Understanding how thermodynamics can be applied in such microscopic settings is of paramount importance for future technologies.”

Colm Gorey

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