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Journal of Physics B Atomic Molecular and Optical Physics

Locality of a class of entangled states

I. R. Senitzky

Published Jul 3, 2002• 3 citations
Publisher

Abstract

The physical meaning of the entanglement of two identical `two-level' atomic dipole oscillators is investigated. Using Schrödinger's equation, the development of entanglement from an initial product state in which one atom is in the upper state and the other in the lower state is exhibited. Examination of the correlation of the oscillations shows that complete entanglement leads to full phase correlation of unknown absolute phase. This property serves to explain the physical meaning of entanglement for the class of systems considered and the results of measurements conducted on them, without resort to the `action at a distance' concept associated with the Einstein-Podolsky-Rosen paradox. A recent experiment in which such entanglement was produced and cited as an illustration of the paradox is analysed and explained by the present theory. It is shown that the Bell inequalities, unlike in experiments on other entangled states, cannot in principle be tested in this type of experiment.

DOI
10.1088/0953-4075/35/14/301

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The physical meaning of the entanglement of two identical two-level' atomic dipole oscillators is investigated. Using Schrödinger's equation, the development of entanglement from an initial product state in which one atom is in the upper state and the other in the lower state is exhibited. Examination of the correlation of the oscillations shows that complete entanglement leads to full phase correlation of unknown absolute phase. This property serves to explain the physical meaning of entanglement for the class of systems considered and the results of measurements conducted on them, without resort to the action at a distance' concept associated with the Einstein-Podolsky-Rosen paradox. A recent experiment in which such entanglement was produced and cited as an illustration of the paradox is analysed and explained by the present theory. It is shown that the Bell inequalities, unlike in experiments on other entangled states, cannot in principle be tested in this type of experiment.
In recent decades it was established that the measurements of physical quantities in space-time points divided by large space-like intervals can be correlated.The correlation is created by the measurements while their mutual influence requires the corresponding supraliminal velocities.This situation is commonly known as the violation of the Bell inequality in the Bohm version of Einstein-Podolsky-Rosen paradox.Nearly 40 years the question remains disputable with a variety of contradicting views.The most frequently the violation is explained by the existence of some momentary action at a distance which obliges the quantum mechanics (as well as all nature) to be nonlocal.We find the "common cause in the past" as the origin of the observed quantum correlation which so far was unnoticed either by the partisans of quantum non-locality or their opponents.The novelty of our approach is the accent on the expressions for the observed physical quantities rather than on the "entangled" two-particle wave functions.We show the crucial role of phases in the correlation process that is hard to notice using the traditional approach.
In recent decades it was established that the quantum measurements of physical quantities in space-time points divided by space-like intervals may be correlated. Though such correlation follows from the formulas of quantum mechanics its physics so far remains unclear and there is a number of different and rather contradictory interpretations. They concern particularly the so-called Einstein-Podolsky-Rosen paradox where the momentary action at a distance together with non-local entangled states is used for the interpretation. We assume that the quantum theory can be formulated as local and look for the consequences of this assumption. Accordingly we try to explain the correlation phenomena in a local way looking for the origin of correlation. To exclude a presupposed correlation of participating quantum particles we consider two independent particle sources and two detectors that are independent as well. We show that the origin of the correlation is the feature that the occupation number of a particle (and other its measurable quantities) is formed by a pair of complex conjugated wave functions with in general arbitrary phases. We consider this point as crucial as it provides interpretation of the observed correlation phenomena that may otherwise look puzzling. We briefly discuss a special type of noise that is typical for the quantum correlation phenomena.
1. Quantum Mechanics, Reality and Separability: Physical Developments of the Einstein-Podolsky-Rosen Argument.- Realism in Quantum Mechanics and a New Version of the EPR Experiment.- Discussion: M. Cini, F. De Martini, K. Kraus, T.W. Marshall, K.R. Popper, H. Rauch, M.C. Robinson, F. Selleri, J. Six, G. Tarozzi, J.-P. Vigier..- The Physical Origin of the Einstein-Podolsky-Rosen Paradox.- Does the Bell Inequality Hold for All Local Theories?.- Is it Possible to Save Causality and Locality in Quantum Mechanics?.- Einstein-Podolsky-Rosen Experiments and Macroscopic Locality.- On the Compatibility of Local Realism with Atomic Cascade Experiments.- Is the Einstein-Podolsky-Rosen Paradox Demanded by Quantum Mechanics?.- Infinite Wave Resolution of the EPR Paradox.- On Non Local Influences.- Einstein Locality for Individual Systems and for Statistical Ensembles.- Can Nondetected Photons Simulate Nonlocal Effects in Two-Photon Polarization Correlation Experiments?.- 2. The Stochastic Interpretation of Quantum Processes.- Quantum Theory of Measurement without Wave Packet Collapse.- A Causal Fluidodynamical Model for the Relativistic Quantum Mechanics.- On the Nonlinear Schrodinger Equation.- Recent Developments in de Broglie Nonlinear Wave Mechanics.- The Role of the Quantum Potential in Determining Particle Trajectories and the Resolution of the Measurement Problem.- When is Statistical Theory Causal?.- Radiation Damping and Nonlinearity in the Pilot Wave Interpretation of Quantum Mechanics.- Stochastic Electrodynamics and the Bell Inequalities.- Nonlocal Quantum-Potential Interpretation of Relativistic Actions at a Distance in Many-Body Problems.- 3. The Realistic Interpretation of the Wave Function: Experimental Tests on the Wave-Particle Dualism.- Third Kind Measurements and Wave-Particle Dualism.- Quantum Effects in the Interference of Light.- Tests of Quantum Mechanics by Neutron Interferometry.- A Unified Experiment for Testing both the Interpretation and the Reduction Postulate of the Quantum Mechanical Wave Function.- Epilogue.- Evolutionary Epistemology.
We first consider the Einstein-Podolsky-Rosen (EPR) paradox for the system of two particles with spin 1/2 with entangled spins in first-quantized quantum mechanics (QM). If measurement is governed by wavefunction collapse, then gedanken experiments show that a number of fundamental principles including conservation of angular momentum and the Heisenberg uncertainty principle can be violated. We conclude that the collapse of the spin part of the wavefunction cannot happen and therefore an EPR paradox does not arise for this system. QM unitarity alone is sufficient to rule out "spooky" action at a distance. The absence of spin wavefunction collapse leads to several interesting conclusions about how measurement works in QM: When wavefunction collapse does not happen, (i) a signal from a macroscopic measuring device indicating that a system is in a state S does not necessarily mean that it is or was in S and (ii) the uncertainty in QM at the microscopic level is transmitted to uncertainty in signals for the macroscopic measuring device. We derive two general results on how quantum measurement works and illustrate them in a spin-1/2 measurement. In contrast to first-quantized QM, in quantum field theory we are unable to fully rule out the possibility of wavefunction collapse. However, when we insist on unitarity (thereby excluding the possibility of wavefunction collapse) and additionally take into account in the wavefunction all degrees of freedom involved in the measurement (including those of the equipment, experimentalists, etc.), a consistant acceptable understanding of the Bell-inequality-type experiments involving entangled photon polarizations emerges including the absence of an EPR paradox. The ability of an experimentalist to be aware of his perceptions but unable to be conscious of other components of a generalized Schrodinger Cat plays a role in resolving the Measurement Problem.
We show that a system of 2n2n2n identical two-level atoms interacting with n cavity photons manifests entanglement and that the set of entangled states coincides with the so-called SU(2) phase states. In particular, violation of classical realism in terms of the Greenberger-Horne-Zeilinger and Clauser-Horne-Shimoni-Holt conditions is proved. We discuss a property of entanglement expressed in terms of local measurements. We also show that generation of entangled states in the atom-photon systems under consideration strongly depends on the choice of initial conditions and that the parasitic influence of cavity detuning can be compensated through the use of Kerr medium.
Most physicists agree that the Einstein–Podolsky–Rosen–Bell paradox exemplifies much of the strange behavior of quantum mechanics, but argument persists about what assumptions underlie the paradox. To clarify what the debate is about, we employ a simple and well-known thought experiment involving two correlated photons to help us focus on the logical assumptions needed to construct the EPR and Bell arguments. The view presented in this paper is that the minimal assumptions behind Bell’s inequality are locality and counterfactual definiteness but not scientific realism, determinism, or hidden variables as are often suggested. We further examine the resulting constraints on physical theory with an illustration from the many-worlds interpretation of quantum mechanics—an interpretation that we argue is deterministic, local, and realist but that nonetheless violates the Bell inequality.