A study of quantum decoherence via spontaneous emission in a system with Kolmogorov-Arnol'd-Moser tori

We present an experimental and numerical study of the effects of decoherenc e on a quantum system whose classical analogue has Kolmogorov-Arnol'd-Moser (KAM) tori in its phase space. Atoms are prepared in a caesium magneto-opt ical trap at temperatures and densities which necessitate a quantum descrip tion. This real quantum system is coupled to the environment via spontaneou s emission. The degree of coupling is varied and the effects of this coupli ng on the quantum coherence of the system are studied. When the classical d iffusion through a partially broken torus is less than or similar to (h) ov er bar, diffusion of quantum particles is inhibited. We find that increasin g decoherence via spontaneous emission increases the transport of quantum p articles through the boundary.