Coherence in quantum chaos, stochastic spacetime, and collective phenomena

Various manifestations of coherence properties in quantum and classical dynamics in open and closed systems are studied. Among many different issues and phenomena related to coherence, particular aspects are expounded by models chosen from quantum chaos, quantum optics, mesoscopic and high energy physics, and semiclassical relativity. I show how coherence in quantum and classical systems manifests itself in different forms and is enhanced, altered, and suppressed in the presence of chaos, randomness, boundary, and environment.; Author's contributions start from the first time discussion of decoherence in quantum cat map and quantum kicked rotor. Wave propagation in stochastic spacetime is considered as that in random media by extending the analogy of spacetime metric with the refractive index of media. Under this analogy, new phenomena inspired by the recent progress in mesoscopic physics are reported. Dynamical symmetry in three-dimensional anisotropic harmonic potential Hamiltonian is used for systematic computation of thermodynamic quantities in Bose-Einstein condensation. Three-step condensation in an anisotropic atom trap is described based on this method. Multistep condensation in relativistic ideal Bose gas in a cavity is also studied.; These phenomena are of potentially observable interest, and they share common features in other areas of physics.