(OpticalSocietyOfAmerica) Researchers in Russia, Switzerland and the United States have formulated a design for a quantum version of Maxwell’s demon that could have some interesting applications in quantum computing and temperature control at the nanoscale. The team’s “extended quantum Maxwell’s demon” would, across a distance as great as five meters, allow a qubit in a mixed quantum state to be replaced with a lower-entropy, pure-state qubit, with no change in energy. The authors see some very practical applications for the work. One such application lies in the realm of quantum computing, where the ability to switch a target qubit’s state from a distance without affecting its energy, using an electromagnetic field, could come in quite handy.
Maxwell’s demon is a thought experiment created by the physicist James Clerk Maxwell in 1867 in which he suggested how the second law of thermodynamics might hypothetically be violated. In the thought experiment, a demon controls a small door between two chambers of gas. As individual gas molecules approach the door, the demon quickly opens and shuts the door so that only fast molecules are passed into one of the chambers, while only slow molecules are passed into the other. Because faster molecules are hotter, the demon’s behavior causes one chamber to warm up and the other to cool down, thereby decreasing entropy and violating the second law of thermodynamics.