Abstract We derive the Gutzwiller’s trace formula by considering the time-evolution operator of the Hamiltonian which describes an N-dimensional time-dependent generalized harmonic oscillator with general force terms, where the time-evolution operator is composed of metaplectic and Weyl-Heisenberg operators. The Hamiltonian is constructed by expanding a wave packet quadratically in position and momentum operators around a reference trajectory. Using the explicit form of the metaplectic operator recently obtained in (2022, J. Korean Phys. Soc. 80, 95), we give the proof of the well known properties of the metaplectic operator, and using those properties, we derive Gutzwiller’s trace formula and investigate the Maslov index appearing in the formula.
The aim of this chapter is to construct the quantum unitary propagator for Hamiltonians which are quadratic in position and momentum with time-dependent coefficients. We show that the quantum evolution is exactly solvable in terms of the classical flow which is linear. This allows to construct the metaplectic transformations which are unitary operators in
L2(Rn) corresponding to symplectic transformations. Simple examples of such metaplectic transformations are the Fourier transform, which corresponds to the symplectic matrix J defined in (3.4) and the propagator of the harmonic oscillator, corresponding to rotations in the phase space. The main results of this chapter are computations of the quantum evolution operators for quadratic Hamiltonians acting on coherent states. We show that the time evolved coherent states are still Gaussian states which are recognized to be squeezed states centered at the classical phase space point (see Chap. 8). From these computations we can deduce most of properties concerning quantum quadratic Hamiltonians. In particular we get the explicit form of the Weyl symbols of the metaplectic transformations. These formulae are generalizations of the Mehler formula for the harmonic oscillator. Quadratic Hamiltonians are very important in quantum mechanics because more general Hamiltonians can be considered as non trivial perturbations of time dependent quadratic ones as we shall see in Chap. 5.