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Physical Review A

Origin of quantum-mechanical complementarity without momentum back action in atom-interferometry experiments

C. S. Unnikrishnan

Published Jun 9, 2000• 8 citations
Publisher

Abstract

We identify the physical origin of the loss of interference pattern in the which-path atom-interferometery experiments that have been discussed widely. The origin of complementarity between the which-path information and the interference pattern is a discrete spinor phase with random sign. This clarifies how complementarity can arise without the Heisenberg back action in momentum.

DOI
10.1103/physreva.62.015601

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We identify the physical origin of the loss of interference pattern in the which-path atom-interferometery experiments that have been discussed widely. The origin of complementarity between the which-path information and the interference pattern is a discrete spinor phase with random sign. This clarifies how complementarity can arise without the Heisenberg back action in momentum.
This article develops an expanded critical-propositional analysis of S. Dürr, T. Nonn, and G. Rempe’s 1998 experiment, “Origin of Quantum-Mechanical Complementarity Probed by a ‘Which-Way’ Experiment in an Atom Interferometer,” published in Nature, in systematic dialogue with the Theory of Objectivity (TO) developed by Vidamor Cabannas and Denivaldo Silva. The Dürr–Nonn–Rempe experiment constitutes an especially significant empirical case because it addresses a foundational question of quantum mechanics: whether the disappearance of interference following the acquisition of which-way information must be explained through mechanical momentum disturbance, as elementary presentations of the uncertainty principle sometimes suggest, or whether complementarity emerges more fundamentally from correlations between distinguishable degrees of freedom. Using an atom interferometer based on rubidium atoms, optical Bragg diffraction, microwave manipulation of hyperfine states, and path marking through internal atomic degrees of freedom, Dürr, Nonn, and Rempe showed that interference can disappear even when the mechanical back action associated with path detection is too small to account for the observed loss of visibility (Dürr, Nonn, and Rempe 1998b). The phenomenon is instead explained through correlations between atomic motion and the internal which-way marker. Their companion quantitative experiment further examined the relation between path distinguishability D and interference visibility V , providing empirical support for the duality relation associated with Englert’s formulation, D 2 + V 2 ≤ 1. The present article examines these results under the modal and methodological discipline proposed by the Theory of Objectivity. It distinguishes three epistemological levels: (1) empirical confirmation of a physical phenomenon; (2) structural compatibility between that phenomenon and categories of the TO; and (3) specific empirical confir- mation of propositions uniquely derived from the TO. This distinction prevents the mistaken inference that an experiment compatible with an axiom thereby demonstrates the axiom’s claimed modal necessity. Particular attention is given to VA4, concerning boundary and distinction; VA5, concerning observation and relational structure; VA6, concerning composition from prior elements and relations; and VA7, concerning the transcendent element understood within the TO as knowledge or information generated in atomic relations and considered equivalent, within the theory, to atomic radiation. The experiment provides a strong empirical demonstration that physically instantiated information can be generated, stored in atomic internal states, correlated with motional alternatives, and associated with measurable changes in interference. This constitutes a potentially important indirect empirical bridge toward the informational dimensions of VA7. Nevertheless, the experiment does not by itself establish the stronger TO proposition that information is ontologically equivalent to atomic radiation, nor does it prove the necessary truth of VA1–VA7. The analysis also considers the phenomenic elements of light, electromagnetic radiation, atomic transitions, information, boundary formation, and observation; the TO concepts of Expansive and Reductive Inducing Effects (EIE/EIR); the cosmogonic theorem; and the theory’s cosmological eras. It argues that the most productive contribution of the Dürr–Nonn–Rempe experiment to the TO is not cosmological but microphysical and methodological. It suggests a possible operational program in which TO concepts of boundary, observation, and informational differentiation are mapped onto measurable quantities such as path distinguishability, coherence, visibility, mutual information, entropy, and state overlap. The resulting assessment is that the Dürr–Nonn–Rempe experiment has a high degree of dialogue with the Theory of Objectivity, particularly through VA4–VA7, while simultaneously exposing an important burden on the TO: to transform philosophical and modal correspondences into mathematically defined, quantitatively testable, and potentially discriminating empirical propositions. Keywords: Theory of Objectivity; quantum complementarity; which-way information; atom interferometry; distinguishability; interference visibility; physical information; quantum correlations; modal ontology; VA4; VA5; VA6; VA7; information and radiation; operational bridges.
Complementarity lies at the heart of conceptual foundation of orthodox quantum mechanics. The wave-particle duality makes it impossible to tell which slit each particle passes through and still observe an interference pattern in a Young's double-slit experiment. In this paper, this duality is appraised under the standard formulation of quantum mechanics for atom interferometers. It is found that the internal freedoms like electronic states of an atom can be used to detect the which-path information of each atom while uphold the interference pattern of atoms when the center-of-mass motion of atoms is detected.
Common sense suggests that a particle must have a definite origin if its full path information is available. In quantum mechanics, the knowledge of path information is captured through the well-established duality relation between path distinguishability and interference visibility. If visibility is zero, high path distinguishability can be achieved, which enables one to determine with high predictive power where the particle originates. We investigate the complementarity between path information and interference visibility through an experiment involving three sources emitting into identical modes. Our findings challenge the classical intuition that a particle can be traced back to its origin through its trajectory when full path information is available. By grouping the crystals in different ways, we demonstrate that it is impossible to ascribe a definite physical origin to the photon pair, even if the emission probability of one individual source is zero and full path information is available. Our results shed new light on the physical interpretation of probability assignment and path information beyond its mathematical meaning and show that the interpretation of path information in quantum mechanics is subjective.
Recent experiments using ultracold atoms arranged in optical lattices have demonstrated controlled transitions between coherent and incoherent photon scattering, reproducing the canonical features of the double-slit experiment without mechanical slits. These results are widely presented as confirmation of quantum complementarity and, in some popular accounts, as refutation of Einstein’s objections to wave–particle duality. In this consilience note, we show that the experiment instead provides strong evidence for a structure-first interpretation, in which wave-like and particle-like behavior emerge as regime descriptions determined by coherence accessibility, not ontological duality or observer action. Interference is lost not through force, recoil, or observation, but through structural redistribution of phase information into inaccessible degrees of freedom. Read in this way, the experiment resolves—not contradicts—Einstein’s original concern, while remaining fully consistent with quantum formalism.
Wave aspects inherent in quantum physics lead to observable consequences, which are far removed from classical intuition. The possibility of interaction-free measurement is one consequence of quantum wave nature at the single particle level. To date, all experiments, which have studied interaction-free measurements, have dealt with modification of the amplitude of the wave function. In this paper, we discuss interaction-free measurements of a second type, where only the phase of the wave function is modified. We show that an example discussed by Penrose is in this class and clarify the physical reasons for loss of interference in such measurements. We discuss the experimental feasibility of interaction-free measurements of the second type, employing micromaser cavities and atom interferometers. One scheme leads to the possibility of interactionfree measurement of the finesse of the cavity by observing atoms that never interacted with the cavity. The loss of interference, in this case, is due to a random spinor phase and there is no Heisenberg momentum back-action. This is the first experimental proposal for interaction-free measurements of pure phase changes.