Abstract
When an atom is coupled to an opto-mechanical system, the evolution of the atom can be significantly modified by the mechanical phonon state. Previously, we showed that the anomalous population inversion can occur in this hybrid system. Here, we show that the quantum state (pure or mixed) of the mechanical mirror can be reconstructed with very high fidelity by measuring the population dynamics of the atom passing through the opto-mechanical cavity. This method may find important applications in the opto-mechanical-based quantum devices.