Quantum Imaging With Undetected Photons and the Theory of Objectivity

This article develops an expanded critical–propositional analysis of Gabriela Barreto Lemos et al.’s experiment, “Quantum Imaging with Undetected Photons,” published in Nature 512 (2014): 409–412, DOI 10.1038/nature13586, in systematic dialogue with the Theory of Objectivity (TO) formulated by Vidamor Cabannas and Denivaldo Silva. Lemos et al. experimentally demonstrated an imaging architecture based on induced coherence without induced emission in which photons that interact with an object are not themselves detected, whereas the image is reconstructed exclusively by detecting photons that never interacted directly with that object. Two coherently pumped nonlinear crystals can produce signal–idler photon-pair alternatives. An idler originating from the first crystal traverses the object and is subsequently mode- matched with the idler alternative associated with the second crystal. Under conditions in which the origin of the generated pair remains physically indistinguishable, the signal alternatives interfere, and amplitude and phase information introduced into the undetected idler path becomes accessible through the detected signal intensity (Lemos et al., 2014; Lahiri et al., 2015). The experiment therefore provides an unusually productive empirical domain in which to examine relations among interaction, physical distinguishability, coherence, information, observation, boundaries, and compositional phenomena. The present study argues that Lemos et al. do not experimentally establish the complete ontology of the Theory of Objectivity and do not demonstrate the modal necessity of its Seven Absolute Truths. Nevertheless, the experiment provides important operational bridges to the Fourth, Fifth, Sixth, and Seventh Absolute Truths when these propositions are carefully distinguished from stronger metaphysical interpretations. Particular attention is devoted to the Fifth Absolute Truth, according to which an element must, for logical existence, be observed or remain within the frequency of at least two other elements, where “observation” does not mean human consciousness. Quantum imaging with undetected photons provides an experimentally controlled domain in which observable manifestation depends on relations among multiple phys- ical systems independently of a conscious observer. The later theoretical analysis of the Lemos architecture showed that information about the object occurs in the interference contribution rather than in either individual signal intensity considered separately (Lahiri et al., 2015). This makes the experiment particularly relevant to a TO interpretation of information as fundamentally relational. Methodological restraint is nevertheless essential. Classical-state correlated optical systems can reproduce important operational features of imaging with unde- tected photons (Shapiro, Venkatraman, and Wong, 2015). Consequently, the Lemos experiment does not by itself discriminate between the ontology of the TO and all competing descriptions. Its strongest scientifically defensible role is therefore to provide a controlled experimental environment in which TO propositions concerning relational existence, physical boundaries, non-human observation, composition, and information may be translated into measurable quantities. The article concludes by proposing an empirical research program in which modal propositions of the TO are related to experimentally measurable parameters such as distinguishability, coherence, visibility, complex transmission, boundary transformation, and recoverable information. Such a program could move the TO from conceptual compatibility with quantum phenomena toward genuinely discriminating empirical predictions.