The Landauer principle asserts that the energy cost of erasure of one bit of information by the action of a thermal reservoir in equilibrium at temperature T is never less than $kTlog 2$. We discuss Landauers principle for quantum statistical models describing a finite level quantum system S coupled to an infinitely extended thermal reservoir R. Using Arakis perturbation theory of KMS states and the Avron-Elgart adiabatic theorem we prove, under a natural ergodicity assumption on the joint system S+R, that Landauers bound saturates for adiabatically switched interactions. The recent work of Reeb and Wolf on the subject is discussed and compared.
