In recent years, physicists have amused themselves by calculating the properties of quantum machines, such as engines and refrigerators.
The essential question is how well these devices work when they exploit the rules of quantum mechanics rather than classical mechanics. The answers have given physicists important new insights into the link between quantum mechanics and thermodynamics.
The dream is that they may one day build such devices or exploit those already used by nature.
Today, Robert Alicki, at the University of Gdansk in Poland, and Mark Fannes, at the University of Leuven in Belgium, turn their attention to quantum batteries. They ask how much work can be extracted from a quantum system where energy is stored temporarily.
Such a system might be an atom or a molecule, for example. And the answer has an interesting twist.
Physicists have long known that it is possible to extract work from some quantum states but not others. These others are known as passive states.
So the quantity physicists are interested in is the difference between the energy of the quantum system and its passive states. All that energy is potentially extractable to do work elsewhere.
Alicki and Fannes show that the extractable work is generally less than the thermodynamic limit. In other words, they show that this kind of system isn’t perfect.
However, the twist is that Alicki and Fannes say things change if you have several identical quantum batteries that are entangled.
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