Mini heat engine could power tomorrow's tiny machines

"Heat engines are devices that turn thermal energy into a useful form known as 'work,'" Ahsan Nazir, a research fellow at the University of Manchester, said in a news release. "Besides being of immense practical importance, the theoretical understanding of factors that determine their energy conversion efficiency has enabled a deep understanding of the classical laws of thermodynamics."

Heat engines are normally studied at the scale of classical physics. But the laws of classical physics aren't always applicable at the nanoscale among quantum states.

Nazir wanted to see how a tiny heat engine would behave in a sub-atomic environment.

"Recently, much interest has focused on quantum realizations of engines in order to determine whether thermodynamic laws apply also to quantum systems," said Nazir.

Previous research has operated on the assumption that the link between the thermal reservoir and the working system -- the heat source and machine -- diminishes as the scales shrink.

"At the classical macroscopic scale this assumption is typically valid -- but we recognized this may not be the case as the system size decreases to the quantum scale," Nazir said.

Nazir and his colleagues created a new theoretical model with which to study thermal engine performance among quantum states, with varying reservoir-system interaction strengths. Researchers used their model to study the behavior of a thermal engine called the four stroke Otto cycle.

"We find that the engine's performance diminishes as the interaction strength becomes more appreciable, and thus non-vanishing system-reservoir interaction strengths constitute an important consideration in the operation of quantum mechanical heat engines," said Nazir.

Nazir and his research partners detailed their findings in the journal Physical Review E.