Dynamical Consequences of Strong Entanglement

Abstract

The concept of motion in quantum theory is reviewed from a didactical point of view. A unitary evolution according to a Schrödinger equation has very different properties compared to motion in classical physics. If the phase relations defining unitary dynamics are destroyed or unavailable, motion becomes impossible (Zeno effect). The most important mechanism is dislocalization of phase relations (decoherence), arising from coupling of a quantum system to its environment. Macroscopic systems are not frozen, although strong decoherence is important to derive quasi-classical motion within the quantum framework. These two apparently conflicting consequences of strong decoherence are analyzed and compared.