Towards fully quantum second laws of thermodynamics: limitations on the evolution of quantum coherences

Understand

The second law of thermodynamics places a limitation into which states a system can evolve into.

• For systems in contact with a heat bath, it can be combined with the law of energy conservation, and it says that a system can only evolve into another if the free energy goes down.
• Recently, it's been shown that there are actually many second laws, and that it is only for large macroscopic systems that they all become equivalent to the ordinary one.
• These additional second laws also hold for quantum systems, and are, in fact, often more relevant in this regime.