Quantum chaos increases too

​That things tend towards chaos is a neat way of summing up the second law of thermodynamics. Knock over a tower and you get a random pile of bricks; but the bricks will never spontaneously build themselves into a tower.

Does this second law still hold for tiny particles such as protons and electrons? And does it apply to situations where there are very few particles?

New research just published in Proceedings of the National Academy of Science (PNAS) by scientists at TU Delft, University College London (UCL), Gdansk University and the
National University of Singapore suggests that the answer is yes; the same, or at least very similar, laws apply at the subatomic level, and even in situations where there are just a few particles.

This is important news – and not just because it underlines a rare connection between classic and so-called quantum physics. These days we live in a world where nano-scale technologies are used to make things at the level of molecules and even atoms; that is smaller than one millionth of a millimetre. Nanotechnology has potential benefits in many fields including water purification, the manufacture of computers and semi-conductors, and the design of drugs. So knowing that even at the quantum level, in situations where there are just a few particles, things still tend towards chaos, and therefore obey the second law of thermodynamics, is of major importance. The second law is sometimes thought of as a statistical law that only holds true when there are huge numbers of particles within a system as in the case of larger, visible, everyday situations. “Imagine we toss a coin thousands of times”, said Dr. Stephanie Wehner of QuTech at TU Delft and one of the team. “In that case, we expect to see more or less as many heads as tails. If you only toss the coin a few times, however, this is not true.

Statistically it could happen that all the coins land tails up. Well, similar phenomena can arise in systems made up of very few particles.” Fewer coin tosses or fewer particles, the results could be different. However this research shows that whether there are many or few particles, the second law still applies.

PhD candidate Nelly Ng (QuTech) said “Our results pave the way towards understanding and analysing the efficiency of even the tiniest quantum machines consisting of just a few particles.”

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