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Full Description
We consider quantum dynamical systems (in general, these could be either Hamiltonian or dissipative, but in this review we shall be interested only in quantum Hamiltonian systems) that have, at least formally, a classical limit. This means, in particular, that each time-dependent quantum-mechanical expectation value X (t) has as i cl Ii -+ 0 a limit Xi(t) -+ x1 )(t) of the corresponding classical sys- tem. Quantum-mechanical considerations include an additional di- mensionless parameter f = iiiconst. connected with the Planck constant Ii. Even in the quasiclassical region where f‾ 1, the dy- namics of the quantum and classicalfunctions Xi(t) and XiCcl)(t) will be different, in general, and quantum dynamics for expectation val- ues may coincide with classical dynamics only for some finite time. This characteristic time-scale, TIi., could depend on several factors which will be discussed below, including: choice of expectation val- ues, initial state, physical parameters and so on. Thus, the problem arises in this connection: How to estimate the characteristic time- scale TIi. of the validity of the quasiclassical approximation and how to measure it in an experiment?
For rather simple integrable quan- tum systems in the stable regions of motion of their corresponding classical phase space, this time-scale T" usually is of order (see, for example, [2]) const TIi. = p,li , (1.1) Q where p, is the dimensionless parameter of nonlinearity (discussed below) and a is a constant of the order of unity.
Contents
Method of Coherent States.- The Exact C-Number Equation for Time-Dependent Expectation Values in Coherent States.- Quasiclassical Perturbation Theory for Time-Dependent Expectation Values with Quantum Nonlinear Hamiltonians.- The Characteristic Times of Violation of Quasiclassical Approximation for Integrable Boson and Spin Systems.- Time-Scale ?? for a Kicked Quantum Nonlinear Oscillator.- The Time of Applicability of the Quasiclassical Approach in a Boson System of Two Interacting Quantum Nonlinear Resonances.- Two Interacting Quantum Nonlinear Resonances in a Spin System.- Quantization of a Stochastic Web.- Characteristic Times for Chaotic Dynamics in Wigner Representation.- Quantum Chaos of Atoms in a Resonant Cavity.- Quantum Chaos of Atoms in a Resonant Cavity Driven by an External Resonant Field.- Violation of the Semiclassical Approximation and Quantum Chaos in a Paramagnetic Spin System.- Weak Quantum Chaos in a System of N Atoms in a Resonant Cavity Interacting with an External Resonant Field.- Quantum Dynamics in Stationary Coherent States (SCS).- Discussion.
