Atomic Cascade Experiments Research Articles

Nonlocality in quantum mechanics and atomic-cascade photons

It is shown that the conjunction of Einstein's locality with a supplementary assumption leads to a constraint that is sometimes grossly violated by the quantum mechanical probabilities in the case of atomic-cascade experiments. This supplementary assumption is weaker and more general than the supplementary assumption of Clauser and Horne.

Possible solution for EPR paradox in atomic cascade experiments

Polarization measurements in atomic cascades are described by following a quantum mechanical analysis. Violation of Bell inequalities for these measurements may follow from correlations introduced by the measurement process and not from action at a distance.

The compatibility between quantum mechanics and local realist theories in atomic cascade experiments

The authors show that the divergence between the predictions of quantum optics and the local realist theory known as stochastic optics, for the extended type of photon-coincidence experiment described recently by deCaro, is of the same order of magnitude as for Aspect-type experiments. This means that, in such new experiments, as in those so far performed, counting statistics will have to be greatly improved before a discrimination between the two theories becomes possible. The authors also show that the outstanding difference between the two theories is that, while stochastic optics uses a genuine, that is, positive, detection probability, the corresponding quantum formalism leads to a pseudoprobability. Nevertheless there is a striking parallel, in that both theories recognize the phenomenon known as enhancement, and both describe it as having its origin in a mixing of the signal field with the zero-point field by a polarizing device.

What does noise do to the bell inequalities?

We show that a semiclassical theory which takes account of vacuum fluctuations of the electromagnetic field is capable of giving a fully local realist description of the coincidence data from atomic-cascade experiments. Such a theory explains, in a unified manner, why there is a natural upper limit on detector efficiency, and also why, for certain values of the “hidden” variables, there is enhancement of the detection efficiency.

Quantum mechanics as the limit of a symmetric local theory

It is shown that the quantum-mechanical spin-correlation function of the photon pairs emitted in atomic cascade experiments can be obtained by a limiting process from a local realistic theory which is symmetric between the analyzers.

Local hidden variable theories cannot be tested by atomic cascade experiments

A local hidden variable model predicting exact agreement with quantum mechanics in all experiments with correlated photon pairs is proposed. It proves that local hidden variable theories cannot be refuted by atomic cascade experiments.

A stochastic local realist model for the EPR atomic-cascade experiment which reproduces the quantum-mechanical coincidence rates

We show that a recent model of Barut and Meystre is not local realist, but that by suitable modification it besomes one for the particular case of EPR atomic-cascade experiments, using either one-channel or two-channel analyzers. It exhibits clearly the enhancement property necessary for a model violating the second Clauser-Horne inequality. It satisfies the Bell inequality, and it may be used to understand more clearly that the quantum model for real analyzers also satisfies this inequality.

Experimental tests of bell inequalities. Are all local models really excluded?

Bell inequality tests performed by atomic cascade experiments always make use of a coincidence counting electronics. It is shown that such electronics can act as a “source of nonlocality” in the correlation function, even if every phenomenon involved is perfectly local. A simple example illustrating this situation is given.

Local realist model for the coincidence rates in atomic-cascade experiments

We assume that the two photons emerging from an atomic cascade process are classical wave-packets with well defined intensities and states of elliptical polarization. Such weak light signals, when interacting with optical devices such as linear polarizers and quarter-wave plates, are assumed to undergo stochastic changes of intensity in addition to the change in polarization experienced by macroscopic signals. We show how such assumptions can lead, in a natural way, to an enhancement in the detection probability of certain signals, and hence to a family of models which fit the observed counting rates in all atomic-cascade experiments so far performed, including those which investigate the circular polarizations of the photons.

Testing for reality with atomic cascades

The family of local realist models which is excluded by the data from atomic-cascade experiments of the Clauser-Freedman or Aspect type is very much smaller than those experimenters supposed. Nevertheless, we show that, with somewhat longer experimental runs and an improved method of data analysis, it is possible to discriminate between the predictions of the quantum model and those of a large new family of local realist models. In particular, if the coincidence count with polarizers parallel exceeds 7 × 10 4, then the single-parameter family discussed in a previous letter may be tested against the quantum model.

Local realism has not been refuted by atomic cascade experiments

Abstract We obtain a local realistic model, involving just one angular hidden variable, giving predictions, for the coincidence counts in atomic cascade experiments, which come extremely close to those of the quantum-mechanical model, and which fit the experimental data as closely as do the predictions of that model.