At An Atomic Level;Even Thermodynamics Gets Strange

Ice cubes melt and hot coffee cools. This is the easiest way of the world, protected in the laws of thermodynamics. Left behind to its own devices, things incline to reach the same temperature, known as Thermodynamic equilibrium.

But things are not so straightforward when we study individual atoms. Scientists at University of California, Los Angeles (UCLA), have studied the method of buffer gas cooling, a technique used to cool ions by dipping them in clouds of cold atoms. In the old-fashioned picture, the cold atoms should take some energy from the ions and you should finish up with cooler ions. This, however, is not permanently the case. In a paper printed in Nature Communications, the scientists discovered that the ending temperature of the ions depended on the original temperature, but depended also on the number of ions.

Co-author Professor Eric Hudson said in a statement, "This apparent departure from the familiar laws of thermodynamics is similar to our warm apple pie either cooling as expected or spontaneously overflowing into flames, depending on the pie's particular temperature when it is placed in the window."

In this specific study, the team tried to cool up to 10 barium ions by dipping them in a cloud of 3 million laser cooled calcium atoms. Once the calcium cloud was detached, the ions should have cooled down, but at times they did not. The method is in many respects a contracted fridge. There is a coolant (the cold atoms) taking away the heat from something new. Unfortunately, at that level, there are non-equilibrium happenings at play. Buffer gas cooling must be more nuanced than previously supposed; the difficulty of the whole system must be taken into description.

Lead author Steven Schowalter, who worked in Hudson's Laboratory, added "Our results determine that you cannot just throw any buffer gas into your device , no matter how cold it is, and expect it to work as an operative coolant."

This finding is apparently not a violation of the laws of Thermodynamics, but it indicates that even well-established methods can go a bit groovy when we move into the micro-world. As buffer gas cooling is used in many unlike applications, from forensics to anti-matter production, it is necessary to understand the full story.