To effectively control and study ions, scientists must cool the high-energy particles. To do so, they rely on a basic premise of the laws of thermodynamics -- that an object with a higher temperature will eventual cool to the same temperature as its surroundings. An apple pie, for example, will eventually cool to room temperature.

To cool ions, researchers immerse them in clouds of super-cooled gas molecules. Most of the time, scientists are unconcerned with the final temperature of the ions. They're just trying to cool them enough to more easily manipulate them.

Scientists at the University of California Los Angeles tracked the entire ion cooling process and found the particles never truly cool to the temperature of the surrounding gas molecules. Further experimentation showed that under certain conditions cooling ions settle on one of two final resting temperatures depending on their original temperatures.

"This apparent departure from the familiar laws of thermodynamics is akin to our warm apple pie either cooling as expected or spontaneously bursting into flames, depending on the pie's exact temperature when it is placed in the window," Eric Hudson, associate professor of physics at UCLA, said in a news release.

Scientists used lasers to super-cool 3 million calcium atoms to just above absolute zero and then allowed them to mix with 10 barium ions in a closed system. When the system reached its final resting temperature, the scientists extracted the ions and found varying final temperatures, which were dependent on starting temperature and ion number.

The results show that the hybrid atom-ion trap cooling method yields nonequilibrium behavior.

Researchers detailed the departure from the laws of thermodynamics in the journal Nature Communications.

"Of course, this work does not violate the laws of thermodynamics, but it does demonstrate there are still some interesting, potentially useful things to learn about buffer gas cooling," explained John Gillaspy, a physics division program director at the National Science Foundation. "This is the sort of fundamental research that can really guide a wide range of more applied research efforts, helping other scientists and engineers to avoid going down dead-end paths and illuminating more fruitful directions they might take instead."