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Journal of Optics B Quantum and Semiclassical Optics

Nonlocal `interaction-free' reduction of the state vector

Luiz Carlos Ryff, Carlos Henrique Monken

Published Jan 1, 1999• 2 citations
Publisher

Abstract

A nonlocal `interaction-free' experiment is discussed. It is shown that the absence of detection of a photon of a polarization-entangled pair can `force' the other photon of the pair into a well-defined polarization state. Its consequences for a possible ontological interpretation of quantum mechanical formalism are examined.

DOI
10.1088/1464-4266/1/3/309

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A nonlocal interaction-free' experiment is discussed. It is shown that the absence of detection of a photon of a polarization-entangled pair can force' the other photon of the pair into a well-defined polarization state. Its consequences for a possible ontological interpretation of quantum mechanical formalism are examined.
An Einstein-Podolsky-Rosen (EPR)-like argument using events separated by a time-like interval strongly suggestes that measuring the polarization state of a photon of an entangled pair changes the polarization state of the other distant photon. Trough a very simple demonstration, the Wigner-D'Espagnat inequality is used to show that in order to prove Bell's theorem neither the assumption that there is a well-defined space of complete states λλλ of the particle pair and well-defined probability distribution ρ(λ)ρ(λ)ρ(λ) over this space nor the use of counterfactuals is necessary. These results reinforce the viewpoint that quantum mechanics implicitly presupposes some sort of nonlocal connection between the particles of an entangled pair. As will become evident from our discussion, relinquishing realism and/or free will cannot solve this apparent puzzle.
I have been arguing that quantum nonlocality, deeply entrenched in the present formalism of quantum mechanics and widely believed as a reality by physicists, is in fact absent. Spooky nonlocal state reduction is the most, and perhaps the only irrational feature of present day physics. There are experimental results that reject nonlocal state reduction at a distance. Also, there are arguments that show that signal locality itself can be violated if there is true nonlocal collapse of the wavefunction. The Bell's inequalities, the violation of which polarized physicists in favour of nonlocality, arise not due to nonlocality, but due to ignoring prior information on correlations encoded in the phase of local probability amplitudes. Here I discuss an experiment involving particles entangled in energy and time variables that shows that there is no nonlocal state reduction during measurements on entangled particles. Quantum mechanics is inconsistent if it includes the concept of wavefunction collapse as a physical process for entangled multi-particle systems.
We have performed a series of experiments using a spontaneous parametric down-conversion source to produce pairs of photons in either entangled or non-entangled polarization states. We determine the full quantum mechanical polarization state of one photon, conditioned on the results of measurements performed on the other photon. For non-entangled states, we find that the measured state of one photon is independent of measurements performed on the other. However, for entangled states, the measured state does depend on the results of measurements performed on the other photon. This is possible because of the nonlocal nature of entangled states. These experiments are suitable for an undergraduate teaching laboratory.
We investigate direct observation of quantum nonlocality without reference to theoretical models (including Bell theorem) except quantum mechanics, with a bipartite polarization-entangled state in which one photon immediately reduces into a circular-polarization (CP) state after its partner is detected in another CP state. Of essence is the mechanical detection of the CP state of a photon that carries angular momentum and exerts a torque on a half-wave plate whose mechanical motion is then varied. If implemented, the model-independent observation of quantum nonlocality violates Lorentz invariance in experiment and may indicate new fundamental physics beyond the Standard Model.