Chaos and Generalized Multistability in Quantum Optics

A challenging problem in non-equilibrium statistical mechanics is that regarding the insurgence of ordered structures starting from a chaotic (maximum entropy) condition, in a system strongly perturbed at its boundary as a quantum optical system. For still higher perturbations, the ordered structures become more and more complex, until reaching deterministic chaos. Three experimental situations for CO₂ lasers (a laser with modulated losses, a ring laser with competition between forward and backward waves, and a laser with injected signal) are analyzed as examples of the onset of chaos in systems with a homogeneous gain line and with a particular time scale imposed by the values of the relaxation constants. I stress the coexistence of several basins of attraction (generalized multistability) and their coupling by external noise. This coupling induces a low frequency branch in the power spectrum. Comparison is made between the spectra of noise-induced jumps over independent attractors and that of deterministic diffusion within subregions of the same attractor. At the borderline between the two classes of phenomena a scaling law holds, relating the control parameter and the external noise in their effect on the mean escape time from a given stability region.