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arXiv:1808.05165 · Results in Physics

Energy transfer and position measurement in quantum mechanics

J.C. Ye, S.Q. Kuang, Z. Li, Shangzhe Dai, Quanhui Liu

Published Feb 23, 2019• 11 citations
arXivHTMLPDF

Abstract

The Dirac delta function can be defined by the limitation of the rectangular function covering a unit area with decrease of the width of the rectangle to zero, and in quantum mechanics the eigenvectors of the position operator assume the form of the delta function. When discussing the position measurement in quantum mechanics, one is tempting to take the mathematical convention that uses the rectangular wave function of sufficiently narrow width to approximate the delta function in order to making the state of the position physical. We argue that such an approximation is improper in physics, because during the position measurement the energy transfer to the particle might be infinitely large. The continuous and square-integrable functions of both sharp peak and sufficiently narrow width can then be better approximations of the delta function to represent the physical states of the position. When the slit experiment is taken as an apparatus of position measurement, no matter what potential is used to model the slit, only the ground state of the slit-dependent wave function matters.

DOI
10.1016/j.rinp.2019.02.060

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It is well-accepted that the Dirac delta function can be defined by the limitation of the square function covering a unit area with decrease of the width of the square to zero, and the eigenvectors of the position operator take the form of the delta function. When discussing the position measurement in quantum mechanics, one is prompted by the mathematical convention that uses the square function of sufficiently narrow width to approximate the delta function in order to making the state of the position physical. We argue that such an approximation is improper in physics, because during the position measurement the energy transfer to the particle might be infinitely large. The continuous and square-integrable functions of both sharp peak and sufficiently narrow width can then be better approximations of the delta function to represent the physical states of position.

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Paper 74 — No Quantum Superposition This paper argues, by reductio ad absurdum, that the physical realisation of superposition — simultaneous multi-location existence — is incompatible with seven independent and well-established physical principles: (1) the observational fact that no infinite physical quantity has ever been measured; (2) conservation of energy; (3) the mass-energy equivalence E = mc²; (4) the Bekenstein entropy bound; (5) the second law of thermodynamics; (6) the Heisenberg uncertainty principle; and (7) causality. The foundational identification is that information, energy, and mass stand in proportional existential relation (Bekenstein bound: I ∝ M; Landauer principle: ΔE ∝ ΔI; mass-energy equivalence: E = mc²). Complete superposition requires infinite information processing, and therefore infinite energy and infinite mass — quantities universally absent from the observational record of physics. 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The disappearance of the interference pattern upon which-path measurement is explained without wavefunction collapse: the measurement interaction physically disrupts the matter wave's coherent two-slit propagation. Three experimentally testable predictions distinguish this framework: (1) weak-measurement trajectory reconstruction should reveal single-path trajectories inconsistent with simultaneous two-slit passage; (2) diffraction fringe spacing should depend on the mass density of the slit material, because denser slit edges generate a steeper refractive-index gradient; (3) the fringe pattern should exhibit a density-dependent phase shift measurable with current matter-wave interferometry technology. The Schrödinger equation and Born's rule are retained without modification. Paper 76 — Discriminating Experiments for the Constructive-Interference Account of Gravity This paper derives the specific numerical values predicted by Paper 29 — n(r) from the Schwarzschild metric, Δφ = k₀∫[n₁(r)−n₂(r)]dr from the medium-structure integral, and Δx_max = f(∇n, geometry, λ₀) from the interference structure — and assesses whether current experimental technology can measure the gap between Paper 29's predictions and standard QM's predictions. Three formal conditions for a discriminating experiment are established: structural absence of the variable from standard QM, signal exceeding current resolution, and impossibility of alternative explanation. Two experimental classes satisfy all three conditions with existing apparatus: COW path-geometry (predicted δ(Δφ) ~ 10⁻³ rad vs. resolution ~10⁻⁴ rad, path shape structurally absent from the standard COW formula) and slit-material density (predicted Δx_max ~ tens of nm vs. resolution 1–5 nm, material density structurally absent from Δy ≈ λL/a). Cumulative agreement across both systems constitutes genuine inductive support for the proposed mechanism. Paper 77 — From Electrons to Fullerenes This paper addresses three questions that Paper 76 does not: (1) why the slit-material density experiment has never been performed in the hundred years since matter-wave interferometry began — the answer being that standard QM contains no density variable in the slit formula, so experimenters had no reason to vary it, with the Copenhagen prohibition on mechanism questions as the deeper structural reason; (2) why confirmation in exactly two systems — electrons and fullerenes C₆₀ — is sufficient to establish the theoretical outline across six orders of magnitude in mass, because these systems are maximally independent in particle type, mass, apparatus, energy scale, and decoherence environment; (3) what confirmation across this mass range would establish for physics: the first experimentally supported identification of the physical mechanism of gravity, the first experimentally verifiable quantum-gravity connection at accessible energy scales, a physical grounding of Born's rule, and a mechanistic account of the measurement problem. A complete three-layer control protocol for excluding the slit-width confound is specified. Paper 78 — A Three-Dimensional Experimental Matrix This paper extends the experimental programme by introducing slit thickness as a third independent variable alongside matter-wave species and slit-material density. The wave-mechanical account predicts that phase shift scales linearly with slit thickness d: Δφ(ρ,d) = (2π/λ)·[n(ρ)−1]·d — a prediction structurally absent from standard QM, which assigns no physical role to slit thickness. The resulting 5×5×3 matrix of 75 independent measurements has a random coincidence probability of approximately 1/1,728,000, rendering chance agreement with theoretical prediction physically impossible. Three-layer control protocols for fabrication, TEM cross-section verification, and linearity testing are specified for the thickness dimension. Together, the five papers constitute a complete programme: ontological foundation (P74), phenomenological reinterpretation (P75), formal discriminating analysis (P76), strategic and historical argument (P77), and three-dimensional experimental design (P78).

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The Dirac delta function can be defined by the limitation of the rectangular function covering a unit area with decrease of the width of the rectangle to zero, and in quantum mechanics the eigenvectors of the position operator assume the form of the delta function. When discussing the position measurement in quantum mechanics, one is tempting to take the mathematical convention that uses the rectangular wave function of sufficiently narrow width to approximate the delta function in order to making the state of the position physical. We argue that such an approximation is improper in physics, because during the position measurement the energy transfer to the particle might be infinitely large. The continuous and square-integrable functions of both sharp peak and sufficiently narrow width can then be better approximations of the delta function to represent the physical states of the position. When the slit experiment is taken as an apparatus of position measurement, no matter what potential is used to model the slit, only the ground state of the slit-dependent wave function matters.
It is well-accepted that the Dirac delta function can be defined by the limitation of the square function covering a unit area with decrease of the width of the square to zero, and the eigenvectors of the position operator take the form of the delta function. When discussing the position measurement in quantum mechanics, one is prompted by the mathematical convention that uses the square function of sufficiently narrow width to approximate the delta function in order to making the state of the position physical. We argue that such an approximation is improper in physics, because during the position measurement the energy transfer to the particle might be infinitely large. The continuous and square-integrable functions of both sharp peak and sufficiently narrow width can then be better approximations of the delta function to represent the physical states of position.
We review the postulates of quantum mechanics with respect to the representation of physical states and measurable quantities, their time evolution, and the interpretation of measurements. We first formulate the postulates in terms of wave functions and differential operators, and then reformulate them in the abstract Hilbert space of state vectors, using Dirac’s notations. Improper states subject to Dirac’s delta normalization are introduced, and the space of physical states is extended to include them. The postulates are rationalized by associating each Hermitian linear operator with a complete orthonormal system of its eigenvectors, where measurement probabilities depend on the projections of these eigenvectors on the system’s state vector. Particularly, wave functions are identified as projections of state vectors on the position operator eigenstates. State vectors representing multidimensional systems are formulated as tensor products of vectors in their subspaces. Finally, we address the general uncertainty relations in simultaneous measurements of different observables.
According to the postulates of quantum mechanics, the state of a system is associated with a wave function that contains any measurable information on the system at any time. In this chapter we become familiar with wave functions and how they represent the position of particles within the system. Within the realm of quantum mechanics, the position of particles is not deterministic. It is defined by a probability distribution. The wave function is a position-dependent complex-valued amplitude, whose absolute value squared is identified with the probability density for locating the particle in the position space. This identification of the wave function with a probability amplitude imposes some limitation. Particularly, for a closed system in which the particles are bound, the wave function must be proper (square integrable) and normalizable. These properties are discussed and demonstrated for different coordinate systems.
Classical mechanics usually employs two variables x,t to describe motion in the form of x(t). Derivatives of this function yield velocity, acceleration etc. For a bound system, velocity (momentum) changes from one x to the next, but one does not necessarily need time to describe the scenario as one could use the pair of variables p(x),x instead of x(t),t. An issue which arises is that p(x) has double values as it is positive when the bound particle is moving to the right and negative when it is moving to the left. In such a case, time distinguishes between the two motions which occur at the same spatial point. From the point of view of energy, however, such a degeneracy at x is irrelevant because kinetic energy is pp/2m. Thus, it seems one may remove time from a bound state problem as long as one uses an energy (i.e. energy conservation) picture. As a result, we propose using a p(xi), xi model to describe a bound state with p(xi) (momentum at xi) being different at each xi. In order to calculate average of the absolute value of p at xo we suggest using a Dirac delta function delta(p-p(xo)) i.e. related to {Integral dp p delta(p-p(xo))} . If one expands the delta function in terms of the basis exp(ipx), it seems that quantum mechanics for the bound state arises as a classical steady stream picture in terms of energy conservation, with exp(ipx) representing a steady stream picture of a particle with a constant momentum. We discuss informational probability properties of exp(ipx) which make it the basis of choice.
Paper 74 — No Quantum Superposition This paper argues, by reductio ad absurdum, that the physical realisation of superposition — simultaneous multi-location existence — is incompatible with seven independent and well-established physical principles: (1) the observational fact that no infinite physical quantity has ever been measured; (2) conservation of energy; (3) the mass-energy equivalence E = mc²; (4) the Bekenstein entropy bound; (5) the second law of thermodynamics; (6) the Heisenberg uncertainty principle; and (7) causality. The foundational identification is that information, energy, and mass stand in proportional existential relation (Bekenstein bound: I ∝ M; Landauer principle: ΔE ∝ ΔI; mass-energy equivalence: E = mc²). Complete superposition requires infinite information processing, and therefore infinite energy and infinite mass — quantities universally absent from the observational record of physics. Finite N-state superposition is excluded by a complementary argument: maintaining N states simultaneously requires N times the information-processing load of a single undetermined state, violating the principle that nature selects minimum-load configurations. The positive alternative proposed is the undetermined state: during matter-wave propagation, the matter wave is real and physically present, but matter has not yet appeared at any location. This is not a hidden-variable state but an ontological absence of localisation prior to the formation of a constructive interference maximum. Paper 75 — The Double-Slit Experiment Reinterpreted This paper applies the undetermined-state ontology to the paradigmatic demonstration of quantum mechanics. The de Broglie matter wave — a real physical wave — passes through both slits, while the particle remains in an undetermined state until a constructive interference maximum is formed at the detection screen. The disappearance of the interference pattern upon which-path measurement is explained without wavefunction collapse: the measurement interaction physically disrupts the matter wave's coherent two-slit propagation. Three experimentally testable predictions distinguish this framework: (1) weak-measurement trajectory reconstruction should reveal single-path trajectories inconsistent with simultaneous two-slit passage; (2) diffraction fringe spacing should depend on the mass density of the slit material, because denser slit edges generate a steeper refractive-index gradient; (3) the fringe pattern should exhibit a density-dependent phase shift measurable with current matter-wave interferometry technology. The Schrödinger equation and Born's rule are retained without modification. Paper 76 — Discriminating Experiments for the Constructive-Interference Account of Gravity This paper derives the specific numerical values predicted by Paper 29 — n(r) from the Schwarzschild metric, Δφ = k₀∫[n₁(r)−n₂(r)]dr from the medium-structure integral, and Δx_max = f(∇n, geometry, λ₀) from the interference structure — and assesses whether current experimental technology can measure the gap between Paper 29's predictions and standard QM's predictions. Three formal conditions for a discriminating experiment are established: structural absence of the variable from standard QM, signal exceeding current resolution, and impossibility of alternative explanation. Two experimental classes satisfy all three conditions with existing apparatus: COW path-geometry (predicted δ(Δφ) ~ 10⁻³ rad vs. resolution ~10⁻⁴ rad, path shape structurally absent from the standard COW formula) and slit-material density (predicted Δx_max ~ tens of nm vs. resolution 1–5 nm, material density structurally absent from Δy ≈ λL/a). Cumulative agreement across both systems constitutes genuine inductive support for the proposed mechanism. Paper 77 — From Electrons to Fullerenes This paper addresses three questions that Paper 76 does not: (1) why the slit-material density experiment has never been performed in the hundred years since matter-wave interferometry began — the answer being that standard QM contains no density variable in the slit formula, so experimenters had no reason to vary it, with the Copenhagen prohibition on mechanism questions as the deeper structural reason; (2) why confirmation in exactly two systems — electrons and fullerenes C₆₀ — is sufficient to establish the theoretical outline across six orders of magnitude in mass, because these systems are maximally independent in particle type, mass, apparatus, energy scale, and decoherence environment; (3) what confirmation across this mass range would establish for physics: the first experimentally supported identification of the physical mechanism of gravity, the first experimentally verifiable quantum-gravity connection at accessible energy scales, a physical grounding of Born's rule, and a mechanistic account of the measurement problem. A complete three-layer control protocol for excluding the slit-width confound is specified. Paper 78 — A Three-Dimensional Experimental Matrix This paper extends the experimental programme by introducing slit thickness as a third independent variable alongside matter-wave species and slit-material density. The wave-mechanical account predicts that phase shift scales linearly with slit thickness d: Δφ(ρ,d) = (2π/λ)·[n(ρ)−1]·d — a prediction structurally absent from standard QM, which assigns no physical role to slit thickness. The resulting 5×5×3 matrix of 75 independent measurements has a random coincidence probability of approximately 1/1,728,000, rendering chance agreement with theoretical prediction physically impossible. Three-layer control protocols for fabrication, TEM cross-section verification, and linearity testing are specified for the thickness dimension. Together, the five papers constitute a complete programme: ontological foundation (P74), phenomenological reinterpretation (P75), formal discriminating analysis (P76), strategic and historical argument (P77), and three-dimensional experimental design (P78).