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Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields

Minimum-uncertainty states and pseudoclassical dynamics. II

V. Canivell, Pere Seglar

Published Aug 15, 1978• 2 citations

Abstract

The set of initial conditions for which the pseudoclassical evolution algorithm (and minimality conservation) is verified for Hamiltonians of degrees $N$ ($N>2$) is explicitly determined through a class of restrictions for the corresponding classical trajectories, and it is proved to be at most denumerable. Thus these algorithms are verified if and only if the system is quadratic except for a set of measure zero. The possibility of time-dependent $\ensuremath{\alpha}$-equivalence classes is studied and its physical interpretation is presented. The implied equivalence of the pseudoclassical and Ehrenfest algorithms and their relationship with minimality conservation is discussed in detail. Also, the explicit derivation of the general unitary operator which linearly transforms minimum-uncertainty states leads to the derivation, among others, of operators with a general geometrical interpretation in phase space, such as rotations (parity, Fourier).

DOI: 10.1103/physrevd.18.1082

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The set of initial conditions for which the pseudoclassical evolution algorithm (and minimality conservation) is verified for Hamiltonians of degrees

N

(

N>2

) is explicitly determined through a class of restrictions for the corresponding classical trajectories, and it is proved to be at most denumerable. Thus these algorithms are verified if and only if the system is quadratic except for a set of measure zero. The possibility of time-dependent

\ensuremath{\alpha}

-equivalence classes is studied and its physical interpretation is presented. The implied equivalence of the pseudoclassical and Ehrenfest algorithms and their relationship with minimality conservation is discussed in detail. Also, the explicit derivation of the general unitary operator which linearly transforms minimum-uncertainty states leads to the derivation, among others, of operators with a general geometrical interpretation in phase space, such as rotations (parity, Fourier).

All the minimum-uncertainty states $|z(\ensuremath{\alpha})〉$ are built as the eigenstates of generalized annihilation operators $a(\ensuremath{\alpha})$. We obtain the most general Hamiltonian which verfies the following property: Given an initial minimum-uncertainty state $|z(\ensuremath{\alpha})〉$ at

t = 0

, the ${z}^{\ensuremath{'}}$ which corresponds to the minimum-uncertainty state that maximizes ${|〈{z}^{\ensuremath{'}}(\ensuremath{\alpha})|z(\ensuremath{\alpha}),t〉|}^{2}$ follows the classical trajectory in phase space. Finally, we comment on its relationship with the most general Hamiltonian which preserves minimality.

This study discusses the quantum behavior of a particle, which is controlled by fluctuations in the physical space-time (ST) variables, rather than provides a novel interpretation of quantum theory. The fluctuations, i.e., inhomogeneities in a homogeneous phase ST, are prescribed by their probability. They determine the reciprocal space and correlate with the correlation entropy different from zero. Alongside with the minimum entropy, action, and the presence of the Winn-Ehrenfest adiabatic invariant (AI), the fluctuations require the Gilbert information (probabilistic) space linking the physical and the reciprocal ST. Physical quantities in the information space are represented by linear Hermitian operators, which is due to the entropy production in the presence of an AI. Evolution of a quantum system is described by the wave functions having the meaning of information concerning all virtually possible states of a quantum particle. The wave functions are the solutions to the Schrodinger equation and represent a navigation 'roadmap' for the particle to follow. A quantum system is in fact a classical Hamiltonian system in the space of coefficients of the wave function decomposition with respect to the operator eigenfunctions. It is the linearity and the Hermitian nature of the operators which determine the trajectory and the superposition principle in case of the wave behavior of fluctuations. The uncertainty principle, reflects correlation of the fluctuations and, hence, their nonlocality. This study discusses the wave function phase, the Berry phase and its relationship to quantization, discriminability of states and macroscopic quantum effects caused by localization of the particle, followed by a possible entropy change during its transition into a new thermodynamic state.

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

L^2(\mathbb R^n)

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.