Long-range saturation of spatial decoherence in wave-field transport in multiple-scattering media

Summary form only given. Decoherence plays an important role in interpreting the transition from the quantum to the classical world. (And its classical analog determines the transition from wave-like to ray-like optical transport.) The inevitable interaction between the system of interest and the environment makes the superposition of macroscopic states (coherent waves) practically unobservable due to the rapid decoherence between them, and the dynamics of the density matrix (spatial coherence function) provides more detailed interpretations for this "open system" than does the Schrodinger equation, which can only be applied for a closed system. The standard quantum decoherence theory (based on a Fokker-Planck equation) predicts that the density matrix decays exponentially with time (or propagation distance) and that the exponent divided by time ("decoherence rate") is proportional to the square of the separation between two points in the wave field. This cannot be true in the limit of large separation, since then the decoherence rate will be independent of the separation once these two points are sufficiently far away from each other such that the decohering perturbations to the wave field are no longer correlated.