How often do quantum systems violate the second law of thermodynamics? Read more: How often do quantum systems violate the second law of thermodynamics?

The likelihood of seeing #quantumsystems violating the second law of thermodynamics has been calculated by UCL scientists. In two papers, published in this week's issue of Physical Review X ("Fluctuating States: What is the Probability of a Thermodynamical Transition?" and "Fluctuating Work: From Quantum Thermodynamical Identities to a Second Law Equality") and funded by the Engineering and Physical Sciences Research Council, the team determined a more precise version of a basic law of physics - which says that disorder tends to increase with time unless acted on by an outside force - and applied it to the smallest quantum systems. "The vast majority of the time, the second law of thermodynamics is obeyed. It says that a cup of hot coffee in a cold room will cool down rather than heat up, and a collection of coins all initially heads up will likely produce a mixture of heads and tails when given a shake. In fact, it is thanks to the second law of thermodynamics that we instantly recognise when we are watching a movie backwards," explained PhD student Alvaro M. Alhambra (UCL Physics & Astronomy). The team say that situations which break the second law of thermodynamics are not ruled out in principle, but are rare. "We wanted to find out by how much disorder increases, and if disorder sometimes decrease with some probability. These questions become important for small quantum systems where violations of the second law can happen with a significant probability," added co-author Professor Jonathan Oppenheim (UCL Physics & Astronomy).

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