  We study the relaxation of a quantum system towards the thermal equilibrium
using tools developed within the context of quantum information theory. We
consider a model in which the system is a qubit, and reaches equilibrium after
several successive two-qubit interactions (thermalizing machines) with qubits
of a reservoir. We characterize completely the family of thermalizing machines.
The model shows a tight link between dissipation, fluctuations, and the maximal
entanglement that can be generated by the machines. The interplay of quantum
and classical information processes that give rise to practical irreversibility
is discussed.
