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IntechOpen eBooks

Differentiating the Superposition Principle from the Measurable Superposition Effects in Interferometry

Chandrasekhar Roychoudhuri

Published Feb 7, 2019• 2 citations
Publisher

Abstract

The physical interaction processes behind the emergence of dark and bright fringes registered by the detectors at the output of optical interferometers is explained. This knowledge should be helpful to interferometrists to make better physical interpretations of their data. The belief in mysterious “interference of single indivisible photon” will disappear once we recognize that the spatial or temporal energy re-distributions are generated by the physical transformation experienced by the detecting molecules drawing energy from all the light beams. The molecules could be photodetectors at the interferometer output, or the beam combining dielectric boundary. The superposition principle (SP), represented by the linear mathematical sum of two or more wave amplitudes, does not represent an observable phenomenon. The superposition effect (SE), represented by the non-linear square modulus of the joint dipolar stimulation of the detectors by all the superposed waves, is observable. We present two laboratory experiments to clarify these points. Both classical beam combiners and quantum detectors are capable of generating superposition fringes of intensity variations. The logic of “quantumness” of light is narrowly relevant only when a quantum detector deciphers the fringes; it is not valid for classical beam combiners. We will also discuss “entanglement” based on these experiments.

DOI
10.5772/intechopen.81432

Related papers

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The purpose of this paper is to embolden students to raise basic questions regarding the feasibility of “indivisible single photon interference”. We do this by presenting experimental results of well-known classical Mach-Zehnder interferometer (MZI) under two different conditions of beam alignment. We routinely do such experiments in our laboratories. In the first case, we align the light beams on the beam combiner (BC) with their Poynting vectors as perfectly collinear. The 50% dielectric boundary can now transmit 100% of the energy of both the beams into either one of the two MZI output ports, depending upon the relative phase between the two beams combined on the BC from the opposite directions. The dielectric boundary layer actively re-directs the energy from one beam to the other. This is pure classical superposition effect. In the second case, we combine the two beams on the BC with a small intersecting angle. Now the BC functions as a 50% beam splitter to both the beams. One can see spatial fringes as the relative phase varies with spatial distance by placing a photo detector array after the BC. At very low intensity, the quantum properties of the photo detector will become apparent because the photo electrons are discrete and are always bound quantum mechanically to its host molecular assembly; and not because light is definitely quantized. Students can learn to distinguish the pedagogical difference between the Superposition Principle (linear sum of wave amplitudes) and the Superposition Effect (square modulus of the sum of all the wave-induced stimulations) as observable intensity variations due to interaction with materials, classical or quantum.

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Aug 20, 2009•2 citations
The physical interaction processes behind the emergence of dark and bright fringes registered by the detectors at the output of optical interferometers is explained. This knowledge should be helpful to interferometrists to make better physical interpretations of their data. The belief in mysterious “interference of single indivisible photon” will disappear once we recognize that the spatial or temporal energy re-distributions are generated by the physical transformation experienced by the detecting molecules drawing energy from all the light beams. The molecules could be photodetectors at the interferometer output, or the beam combining dielectric boundary. The superposition principle (SP), represented by the linear mathematical sum of two or more wave amplitudes, does not represent an observable phenomenon. The superposition effect (SE), represented by the non-linear square modulus of the joint dipolar stimulation of the detectors by all the superposed waves, is observable. We present two laboratory experiments to clarify these points. Both classical beam combiners and quantum detectors are capable of generating superposition fringes of intensity variations. The logic of “quantumness” of light is narrowly relevant only when a quantum detector deciphers the fringes; it is not valid for classical beam combiners. We will also discuss “entanglement” based on these experiments.
The purpose of this paper is to embolden students to raise basic questions regarding the feasibility of “indivisible single photon interference”. We do this by presenting experimental results of well-known classical Mach-Zehnder interferometer (MZI) under two different conditions of beam alignment. We routinely do such experiments in our laboratories. In the first case, we align the light beams on the beam combiner (BC) with their Poynting vectors as perfectly collinear. The 50% dielectric boundary can now transmit 100% of the energy of both the beams into either one of the two MZI output ports, depending upon the relative phase between the two beams combined on the BC from the opposite directions. The dielectric boundary layer actively re-directs the energy from one beam to the other. This is pure classical superposition effect. In the second case, we combine the two beams on the BC with a small intersecting angle. Now the BC functions as a 50% beam splitter to both the beams. One can see spatial fringes as the relative phase varies with spatial distance by placing a photo detector array after the BC. At very low intensity, the quantum properties of the photo detector will become apparent because the photo electrons are discrete and are always bound quantum mechanically to its host molecular assembly; and not because light is definitely quantized. Students can learn to distinguish the pedagogical difference between the Superposition Principle (linear sum of wave amplitudes) and the Superposition Effect (square modulus of the sum of all the wave-induced stimulations) as observable intensity variations due to interaction with materials, classical or quantum.
The intention of this paper is to underscore that to understand fundamentally new properties of light beams, we must first find the limits of semi classical model to explain optical interference phenomena. We claim that we have not yet reached that limit. Careful analysis of the processes behind detecting fringes indicate that the effect of superposition of multiple optical beams can become manifest only through the mediation of the detecting dipoles. Since the detectors are quantum mechanical, (i) the observed effects are different for different detectors for the same superposed light beams, and further, (ii) they are only capable of registering discrete number of "clicks", whose rate will vary with the incident intensity. A reduced rate of "clicks" at very low intensity does not prove that light consists of indivisible packets of energy. We have also experimentally demonstrated that (i) neither Fourier synthesis, nor, (ii) Fourier decomposition actually model the behavior of EM fields under all possible circumstances. Superposed light beams of different frequencies do not synthesize a new average optical frequency. A pure amplitude modulated pulse does not contain any of the mathematical, Fourier analyzed frequencies. The QED definition of photon being a Fourier mode in the vacuum, it necessarily becomes non-local. Since we have demonstrated that the Fourier theorem has various limitations in classical physics, its indiscriminate use in quantum mechanics should also be critically reviewed.
This chapter explains the basic mathematical framework behind the emergence of the superposition effect as experienced by detectors when simultaneously stimulated by more than one EM wave by modeling the light–matter interaction process in view of the Non-Interaction of Waves property. The growing field of quantum optics does treat the atoms and molecules as quantum dipoles and EM waves mostly as classical waves. The summation of amplitudes implied by the superposition principle is actually carried out by the oscillating dipoles as their single conjoint dipolar stimulation, while constrained by their intrinsic quantum properties. The measurable superposition effects, which are always reported by detectors, are colored by their own unique response characteristics. Thus, one can generate different types of measurable superposition effects simply by changing the quantum characteristics of the detectors.
The interpretation of the detection of very slow rate of photo counts in interference and diffraction experiments have given rise to the prevailing interpretation that photons interfere by themselves and they are indivisible, albeit non-local. The purpose of this paper is to inspire the development of alternate models for the photons by underscoring that, in reality, light does not interfere with light. The effects of superposition, registered as interference fringes, can become manifest only when a suitable detector can respond simultaneously to all the superposed light beams separately arriving from all the paths (or, slits). It should be a strictly causal process. In fact, different detectors with different quantum properties, report different results while exposed to the same superposed fields. Interference and diffraction effects are always observed as fringes through the processes of re-distribution and/or re-direction of the measured energy of the superimposed fields. Accordingly, we present a number of experiments, actual and conceptual, which highlight the contradictions built into the notion of non-locality in interference. A closer examination of these experiments can guide us to develop a conceptually congruent and causal model for both the evolution of photons and the interference (diffraction) effects by adapting to the classical diffraction theory. This theory has been correctly predicting the characteristics of light whether it is star light propagating through the inter galactic space, or nano tip generated light propagating through complex nano photonic waveguides.
We demonstrate the dynamic evolution of superposition effects to underscore the importance of visualizing interaction processes. The model recognizes the principle of Non-Interaction of Waves. Recordable linear fringes, bisecting the Poynting vectors of the two crossing beams, have time evolving amplitude patterns in the bright fringes because the two superposed E-vectors oscillate through zero values while staying locked in phase. If a detector registers steady, stable bright fringes, it must do so by time integration. The QM recipe to model energy exchange by taking the square modulus of the sum of the complex amplitudes has this time integration built into it. Thus, we will also underscore the importance of assigning proper physical processes to the mathematical relationships: the algebraic symbols should represent physical parameters of the interactants and the mathematical operators connecting the symbols should represent allowed physical interaction processes and the guiding force.
This paper extends and generalizes the principle of Non-Interference of Light (NIL) to diffracted secondary wavelets. In a previous series of papers we have demonstrated the NIL principle for well defined superposed light beams, which experience negligible diffracted spreading within the interferometers being used. NIL is consistent with quantum physics where emitted photons from material dipoles are considered non-interacting Bosons. Our NIL principle describes the formation of fringes (energy re-distribution) as patterned energy absorptions or scattering by "local" material dipoles proportional to the square modulus of the sum of all the superposed stimulating fields experienced by the dipoles.