J. Andries, M. De Cock, M. Fannes The Entropy of an Irreversible Quantum Dynamics (49K, LaTeX 2e) ABSTRACT. We consider an irreversible quantum dynamical system that mimics the classical phase doubling map $z\mapsto z^2$ on the unit circle and study its ergodic properties. The main result of the paper is the computation of the dynamical entropy ($\log 2$) using compact perturbations of unity as operational partitions of unity.