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College Physics

Deduction of generalized Ehrenfest theorem by using the entangled state representation

MA Mei-juan

Published Jan 1, 2009• 0 citations
OpenAlex

Abstract

The Generalized Ehrenfest theorem is deduced by using the entangled state representation,that is the common eigenstate of relative coordinate and general momentum of two particles.It is shown that not only quantum mechanics is self-consistent with classical physics,but also the corresponding classical physics law could be deduced by virtue of the quantum mechanics law.

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The Generalized Ehrenfest theorem is deduced by using the entangled state representation,that is the common eigenstate of relative coordinate and general momentum of two particles.It is shown that not only quantum mechanics is self-consistent with classical physics,but also the corresponding classical physics law could be deduced by virtue of the quantum mechanics law.
The eigenstate existing in the problem of EPR paradox is introduced.The commutation of related operators is analyzed and the wave-function in coordinate representation of the eigenstate is verified and its physical signification is discussed.The eigenstate is expended in the direct product space of the moment eigenstates of a two-particle system,subsequently the wave-function in momentum representation is obtained.The relation of the form of the wave-function in momentum representation and the selection of the origin of coordinates,including its physical meaning was analyzed.Results showed that the eigenstate was a entangled state of the coordinate and momentum.
The canonical commutation relation between the quantum mechanical operators of momentum and coordinate and the Ehrenfest theorem in the free particle case are derived solely from the rule of differentiation of the delta function [xδ′(x)=−δ(x)x\delta'(x) = - \delta(x)xδ′(x)=−δ(x)].
The conceptual analysis of quantum mechanics brings to light that a theory inherently consistent with observations should be able to describe both quantum and classical systems, i.e., quantum-classical hybrids. For example, the orthodox interpretation of measurements requires the transient creation of quantum-classical hybrids. Despite its limitations in defining the classical limit, Ehrenfest's theorem makes the simplest contact between quantum and classical mechanics. Here, we generalized the Ehrenfest theorem to bipartite quantum systems. To study quantum-classical hybrids, we employed a formalism based on operator-valued Wigner functions and quantum-classical brackets. We used this approach to derive the form of the Ehrenfest theorem for quantum-classical hybrids. We found that the time variation of the average energy of each component of the bipartite system is equal to the average of the symmetrized quantum dissipated power in both the quantum and the quantum-classical case. We expect that these theoretical results will be useful both to analyze quantum-classical hybrids and to develop self-consistent numerical algorithms for Ehrenfest-type simulations.
Abstract Ehrenfest theorem is extended to the relativistic quantum theory of charged particles, moving under the influence of a classical electromagnetic field. In order to extend the original Ehrenfest result to the relativistic domain we bypassed the problems with the relativistic position operator by deriving directly Newton’s second law. Our approach is characterized by its universality. The detailed form of the wave equation is not needed. All that is required is the existence of the conserved electric four-current built from the particle wave function. The derivation is based on the conservation laws for the energy and momentum.