Generalized gauge independence and the physical limitations on the von Neumann measurement postulate

Feuchtwang, T E; Cutler, P H; Kazes, E

doi:10.1007/BF00732120

Title: Generalized gauge independence and the physical limitations on the von Neumann measurement postulate

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Abstract

An analysis is presented of the significance and consequent limitations on the applicability of the von Neumann measurement postulate in quantum mechanics. Directly observable quantities, such as the expectation value of the velocity operator, are distinguished from mathematical constructs, such as the expectation value of the canonical momentum, which are not directly observable. A simple criterion to distinguish between the two types of operators is derived. The nonobservability of the electromagnetic four-potentials is shown to imply the nonmeasurability of the canonical momentum. The concept of a mechanical gauge is introduced and discussed. Classically the Lagrangian is nonunique within a total time derivative. This may be interpreted as the freedom of choosing a ''mechanical'' (M) gauge function. In quantum mechanics it is often implicitly assumed that the M-gauge vanishes. However, the requirement that directly observable quantities be independent of the arbitrary mechanical gauge is shown to lead to results analogous to those derived from the requirement of electromagnetic gauge independence of observables. The significance of the above to the observability of transition amplitudes between field-free energy eigenstates in the presence (and absence) of electromagnetic fields is discussed. E- and M-gauge independent transition amplitudes between field-free energy eigenstates in the absence ofmore »« less

Authors:: Feuchtwang, T E; Cutler, P H; Kazes, E

Publication Date:: Mon Dec 01 00:00:00 EST 1986

Research Org.:: Pennsylvania State Univ., University Park, PA

OSTI Identifier:: 6921737

Resource Type:: Journal Article

Journal Name:: Found. Phys.; (United States)

Additional Journal Information:: Journal Volume: 16:12

Country of Publication:: United States

Language:: English

Subject:: 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; QUANTUM MECHANICS; GAUGE INVARIANCE; MEASURE THEORY; EIGENSTATES; ELECTROMAGNETIC FIELDS; HAMILTONIANS; HERMITIAN OPERATORS; LAGRANGIAN FUNCTION; PARTICLE MODELS; PROJECTION OPERATORS; SCHROEDINGER EQUATION; TRANSITION AMPLITUDES; AMPLITUDES; DIFFERENTIAL EQUATIONS; EQUATIONS; FUNCTIONS; INVARIANCE PRINCIPLES; MATHEMATICAL MODELS; MATHEMATICAL OPERATORS; MATHEMATICS; MECHANICS; PARTIAL DIFFERENTIAL EQUATIONS; QUANTUM OPERATORS; WAVE EQUATIONS; 657002* - Theoretical & Mathematical Physics- Classical & Quantum Mechanics

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                    Feuchtwang, T E, Cutler, P H, and Kazes, E. Generalized gauge independence and the physical limitations on the von Neumann measurement postulate.  United States: N. p., 1986. 
        Web.  doi:10.1007/BF00732120.

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                    Feuchtwang, T E, Cutler, P H, & Kazes, E. Generalized gauge independence and the physical limitations on the von Neumann measurement postulate.  United States.  https://doi.org/10.1007/BF00732120

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                    Feuchtwang, T E, Cutler, P H, and Kazes, E. 1986.  
        "Generalized gauge independence and the physical limitations on the von Neumann measurement postulate".  United States.  https://doi.org/10.1007/BF00732120.

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@article{osti_6921737,

  title        = {Generalized gauge independence and the physical limitations on the von Neumann measurement postulate},

  author       = {Feuchtwang, T E and Cutler, P H and Kazes, E},

  abstractNote = {An analysis is presented of the significance and consequent limitations on the applicability of the von Neumann measurement postulate in quantum mechanics. Directly observable quantities, such as the expectation value of the velocity operator, are distinguished from mathematical constructs, such as the expectation value of the canonical momentum, which are not directly observable. A simple criterion to distinguish between the two types of operators is derived. The nonobservability of the electromagnetic four-potentials is shown to imply the nonmeasurability of the canonical momentum. The concept of a mechanical gauge is introduced and discussed. Classically the Lagrangian is nonunique within a total time derivative. This may be interpreted as the freedom of choosing a ''mechanical'' (M) gauge function. In quantum mechanics it is often implicitly assumed that the M-gauge vanishes. However, the requirement that directly observable quantities be independent of the arbitrary mechanical gauge is shown to lead to results analogous to those derived from the requirement of electromagnetic gauge independence of observables. The significance of the above to the observability of transition amplitudes between field-free energy eigenstates in the presence (and absence) of electromagnetic fields is discussed. E- and M-gauge independent transition amplitudes between field-free energy eigenstates in the absence of electromagnetic fields are defined. It is shown that, in general, such measurable amplitudes cannot be defined in the presence of externally applied time-dependent fields. Transition amplitudes in the presence of time-independent fields are discussed. The path dependence of previous derivations of E-gauge independent Hamiltonians and/or transition amplitudes in the presence of electromagnetic fields are related to the inherent M-gauge dependence of these quantities in the presence of such fields.},

  doi          = {10.1007/BF00732120},

  url          = {https://www.osti.gov/biblio/6921737},
  journal      = {Found. Phys.; (United States)},
number       = ,

  volume       = 16:12,

  place        = {United States},

  year         = {Mon Dec 01 00:00:00 EST 1986},

  month        = {Mon Dec 01 00:00:00 EST 1986}

}

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