Composite Complex Quantum Systems

We now consider level grouping in multilevel systems other than the one-dimensional relay of isolated levels discussed in the previous chapter. The population dynamics of such systems can display various manifestations that are typical of the systems already considered, such as exponential decay at short times, quantum recurrences and revivals, cooperative behavior, and quantum localization. Such systems can also demonstrate diffusive behavior. Typically, a problem of this type does not correspond to any hidden symmetry resulting in specific commutation relations among different parts of the Hamiltonian that comprise a closed subalgebra, and the evolution occurs in the entire Hilbert space, being constrained only by energy conservation.