Maxwell’s Demon Joins the Quantum Revolution

Researchers at the University of New South Wales, Sydney have a announced a new technique that improves the probability of successfully resetting the a quantum bit using what they call “a modern version of Maxwell’s demon.”

Maxwell’s demon was a thought experiment devised by the renowned physicist James Clerk Maxwell in 1867. The term refers to a theoretical “finite thing” (later dubbed a “demon” by Lord Kelvin) that opens and closes a door in a two-sided box to locate fast-moving (hot) gas molecules in one chamber and the slow moving (cold) molecules in the other. According to Maxwell, locating the hot molecules on one side and the cold ones on the other would reduce the total entropy of the system, which would violate the 2^nd law of Thermodynamics.

Modern-day quantum computers require a very low energy state to reliably reset the qubit to its zero state, which is one reason why quantum computers typically operate close to absolute zero. Professor Andrea Morello of UNSW Sydney described their spin on Maxwell’s demon as follows, “...we used a much more modern ‘demon’ – a fast digital voltmeter – to watch the temperature of an electron drawn at random from a warm pool of electrons. In doing so, we made it much colder than the pool it came from, and this corresponds to a high certainty of it being in the ‘0’ computational state.”

The technique provided a 20x improvement in the probability of the quantum bit reaching the zero state.