We describe a minimal model of a quantum Maxwell demon obeying Hamiltonian
dynamics. The model is solved exactly, and we analyze its steady-state
behavior. We find that writing information to a quantum memory induces a
probability current through the demon, which is the quantum analog of the
classical Maxwell demon's action. Our model offers a simple and pedagogical
paradigm for investigating the thermodynamics of quantum information
processing.Comment: 7 pages, 8 figures; accepted for publication in Physical Review