On the uniform convergence of ergodic averages for $C^*$-dynamical systems

Abstract

We investigate some ergodic and spectral properties of general (discrete) $C^*$-dynamical systems $({\mathfrak A},\Phi)$ made of a unital $C^*$-algebra and a multiplicative, identity-preserving $*$-map $\Phi:{\mathfrak A}\to{\mathfrak A}$, particularising the situation when $({\mathfrak A},\Phi)$ enjoys the property of unique ergodicity with respect to the fixed-point subalgebra. For $C^*$-dynamical systems enjoying or not the strong ergodic property mentioned above, we provide conditions on $\lambda$ in the unit circle $\{z\in{\mathbb C}\mid |z|=1\}$ and the corresponding eigenspace ${\mathfrak A}_\lambda\subset{\mathfrak A}$ for which the sequence of Cesaro averages $\left(\frac1{n}\sum_{k=0}^{n-1}\lambda^{-k}\Phi^k\right)_{n>0}$, converges point-wise in norm. We also describe some pivotal examples coming from quantum probability, to which the obtained results can be applied.