Photoisomerization in a dissipative environment
Chang-Qin Wu
Department of Physics, Fudan University, Shanghai, 200433, P.R. China

We study the effects of dissipation on photoisomerization (PI). The result suggests the existence of two types of environment depending on whether it ``entangles'' with the molecule. With entanglement there is a quantum phase transition between a state where PI persists, to a state where PI is quenched by the environment. Without entanglement the environment only quantitatively modifies the PI behavior. We discuss the relevance of our results to a recent STM experiment, and predict the signature of the quantum phase transition in optical absorption spectra.