Quantum dissipation is a dynamical collective effect

We show that the dissipative dynamics observed in a small quantum system coupled to a large one (the bath) is a consequence of increasing the size of the bath. We exemplify this effect with a quantum harmonic oscillator coupled to N harmonic oscillators. We find that revivals in the level population exist and give an estimate of their period. For large values of N, the level population decays exponentially coming into thermal equilibrium. We conclude that quantum dissipation is a dynamical collective effect. Finally, we discuss extensions beyond the harmonic oscillator.