Section: New Results

Observing a quantum Maxwell demon at work

Participants: R. Azouit, B. Huard and P. Rouchon

The results of this section were published [14]

In apparent contradiction to the laws of thermodynamics, Maxwell's demon is able to cyclically extract work from a system in contact with a thermal bath exploiting the information about its microstate. The resolution of this paradox required the insight that an intimate relationship exists between information and thermodynamics. Here, this Maxwell demon experiment tracks the state of each constituent both in the classical and quantum regimes. The demon is a microwave cavity that encodes quantum information about a superconducting qubit and converts information into work by powering up a propagating microwave pulse by stimulated emission. Thanks to the high level of control of superconducting circuits, direct measurements (combined with maximum-likelihood estimation techniques inspired by  [90]) give the extracted work and entropy remaining in the demon's memory. This experiment provides an enlightening illustration of the interplay of thermodynamics with quantum information.