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Phase-Shifted Bell States

Carey L. Jackman, Paul Werbos, Maarten D. Hoogerland, Rainer Leonhardt, Jeffery Jonathan Joshua Davis

Published Oct 1, 2025• 0 citations
OpenAlex

Abstract

Abstract - We prepare a system of two photons in phase shifted entangled states by setting a quarter wave plate on one path to angles different than 0 or 90 degrees, thereby phase-shifting part of the entangled photon states. We report the results of polarization correlation experiments with some intriguing questions about how to interpret them, with future possible application in quantum information, communication and computation.

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Abstract - We prepare a system of two photons in phase shifted entangled states by setting a quarter wave plate on one path to angles different than 0 or 90 degrees, thereby phase-shifting part of the entangled photon states. We report the results of polarization correlation experiments with some intriguing questions about how to interpret them, with future possible application in quantum information, communication and computation.
Inspired by previous studies and pioneers of the field, we present new results on an extensive Einstein, Podolsky, and Rosen (EPR)–Bell experiment using photons generated by parametric down-conversion, where one of the photons is deliberately phase-shifted. Our experiments show some surprising results for particular angles of this phase shift, where, for some states, the Clauser, Horne, Shimony, and Holt inequality shows no violations, requiring us to review our understanding of “entangled” states vis-à-vis the correlations obtained via experimental coincidence counts in agreement with quantum mechanics theoretical predictions. We give some possible explanations about the correlated states that show no violations of these inequalities.
Two-photon polarization-correlation measurements have been performed in order to test local realism under conditions in which the two photons pass through quarter-wave plates before reaching the polarizers. The motivation for this experiment is the fact that two previous experiments with quarter-wave plates preceding the polarizers failed to observe statistically significant violations of locality [J. F. Clauser, Nuovo Cimento 338, 740 (1976); A. J. Duncan, H. Kleinpoppen, and Z. A. Sheikh, in Bell's Theorem and the Foundations of Modern Physics, edited by A. van der Merwe, F. Selleri, and G. Tarozzi (World Scientific, Singapore, 1992), p. 161]. We find that the Clauser-Horne type of Bell inequality is violated by about 40 standard deviations. Possible reasons for the failure of earlier experiments are discussed.
We describe an experiment where the phase and amplitude of the interference pattern of light going through an interferometer was varied by doing operations on quantum-correlated light that did not go through the interferometer. This was accomplished by sending a pair of polarization-entangled photons in separate directions, one to an interferometer and the other one to a phase shifter, in principle in a remote location. The interferometer was set up to put the state of the pair in a superposition of maximally entangled states. The phase shifter inserted a phase between the product-state components that made up each entangled state. Polarizers located before the detectors projected the quantum state of the light. As a result, the phase and amplitude of the interference pattern were varied by changing the settings of the phase shifter and polarizer in the path of the photon in the remote location.
We propose a scheme capable of performing complete Bell-state analysis for a single-photon hybrid entangled state. Our single-photon state is encoded in both polarization and frequency degrees of freedom. The setup of the scheme is composed of polarizing beam splitters, half wave plates, frequency shifters, and independent wavelength division multiplexers, which are feasible using current technology. We also show that with this setup we can perform complete two-photon Bell-state analysis schemes for polarization degrees of freedom. Moreover, it can also be used to perform the teleportation scheme between different degrees of freedom. This setup may allow extensive applications in current quantum communications.
This paper conveys briefly and concisely what could be the implications of the Einstein-Bohr debate when we consider the results of Phase-Shifted EPR-Bell states from a study conducted in Maarten Hoogerland’s Lab in the Dodd-Walls Centre for Photonics and Quantum Technologies, University of Auckland, New Zealand (2018-2024). The results of this study were presented at the first Biological Physics and Meaning Mini Conference on ‘QUANTUM MECHANICS, THE MEASUREMENT PROBLEM AND HUMAN CONSCIOUSNESS’ (Feb. 2024). Here, I also examine the nature of correlated pairs of photons produced by Spontaneous Parametric Down Conversion (SPDC) Type II, when the photon of one path is altered with a Quarter Wave Plate (QWP), shifting the polarization from linear to elliptical or circular. As stated in the above mentioned study, surprisingly, some of these Phase Shifted Bell states (correlated pairs) produce no violation of the Clauser, Horne, Shimony and Holt (CHSH) inequality, raising yet again a question mark on the meaning of ‘entanglement’ when understood as ‘spooky action at a distance’, in the context of the formalism of Quantum Mechanics and the different associated interpretations. If ‘spooky action at a distance’ is ruled out from physical systems and we consider new more general stochastic laws, then we open the way for a more interesting future physics on the side of Einstein and realism that, under some regimes, may manifest as nonlocality in terms of information structures. Perhaps, religious, spiritual and mystical experience (RSME) may have a place in physics and the sciences in general, as experienced information and meaning within physical restrictions in a classically consciously experienced lived life in spacetime.