Maxwell’s Demon Meets Nonequilibrium Quantum Thermodynamics

In 1867, James Clerk Maxwell imagined a “neat fingered” being with the ability to sort particles in a gas based on their speed [1]. Maxwell’s demon, as the being became known, could quickly open and shut a trap door in a box containing a gas and let hot particles through to one side of the box but restrict cold ones to the other. At first glance, this scenario seems to contradict the second law of thermodynamics, as the overall entropy appears to decrease. Almost 150 years on, Maxwell’s paradox, which was only properly understood a century after its original inception, continues to inspire physicists. In particular, there is currently a large activity in trying to understand the thermodynamics of devices that operate in the quantum domain and are out of thermal equilibrium, and how a unit like Maxwell’s demon may be used to control them and enhance their performance. Roberto Serra from the Federal University of ABC, Brazil, and colleagues [2] have now implemented a Maxwell’s demon that can control and rectify entropy production in a quantum system driven out of thermal equilibrium (Fig. 1). This finding paves the way to achieving the ultimate goal of complete control of nonequilibrium quantum systems at the nanoscale and beyond.