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Emilio Santos

Publications and source records attributed to Emilio Santos.

At least 55 records · Page 3Linked to original sources
arXiv2008

Preliminary analysis of a recent experiment by F. A. Bovino

An analysis is made of the results of a recent polarization correlation experiment by Bovino (unpublished) where about 60,000 data have been obtained. I assume that the state of the photon pairs produced in the source (a non-linear crystal) are in a (slightly)non-maximally entangled state and the most relevant non-idealities of the set-up are taken into account. A comparison is made between the predictions of quantum mechanics and a simple family of local hidden varaibles models with the result that the former is violated by more than 4 standard deviations whislt the data are compatible with the family of local models.

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arXiv2007

A classical model for a photodetector in the presence of electromagnetic vacuum fluctuations

The main argument against the reality of the electromagnetic vacuum fluctuations is that they do not activate photon detectors. In order to meet this objection we propose a classical model of a photodetector which, in the simple case of a light signal with constant intensity, gives a counting rate which is a non-linear function of the intensity. For sufficiently large signal intensity, the counting rate is proportional to the intensity, in agreement with the standard quantum results, but there is a dark rate when the signal intensity is low.

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arXiv2004

Bell's theorem and the experiments: Increasing empirical support to local realism

It is argued that local realism is a fundamental principle, which might be rejected only if experiments clearly show that it is untenable. A critical review is presented of the derivations of Bell's inequalities and the performed experiments, with the conclusion that no valid, loophole-free, test exists of local realism vs. quantum mechanics. It is pointed out that, without any essential modification, quantum mechanics might be compatible with local realism. This suggests that the principle may be respected by nature.

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arXiv2004

Entropy inequalities and Bell inequalities for two-qubit systems

Sufficient conditions for (the non-violation of) the Bell-CHSH inequalities in a mixed state of a two-qubit system are: 1) The linear entropy of the state is not smaller than 0.5, 2) The sum of the conditional linear entropies is non-negative, 3) The von Neumann entropy is not smaller than 0.833, 4) The sum of the conditional von Neumann entropies is not smaller than 0.280.

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arXiv2004

Optical tests of Bell's inequalities not resting upon the absurd fair sampling assumption

A simple local hidden-variables model is exhibited which reproduces the results of all performed tests of Bell\'{}s inequalities involving optical photon pairs. For the old atomic-cascade experiments, like Aspect\'{}s, the model agrees with quantum mechanics even for ideal set-ups. For more recent experiments, using parametric down-converted photons, the agreement occurs only for actual experiments, involving low efficiency detectors. Arguments are given against the fair sampling assumption, currently combined with the results of the experiments in order to claim a contradiction with local realism. New tests are proposed which are able to discriminate between quantum mechanics and a restricted, but appealing, family of local hidden-variables models. Such tests require detectors with efficiencies just above 20%.

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arXiv2002

How photon detectors remove vacuum fluctuations

The main argument against the reality of the electromagnetic quantum vacuum fluctuations is that they do not activate photon detectors. In order to met this objection I propose a model of photocounting which, in the simple case of a light signal with constant intensity, predicts a counting rate proportional to the intensity, in agreement with the standard quantum result.

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arXiv2002

Can quantum vacuum fluctuations be considered real?

The main argument against the assumption that quantum fluctuations of the electromagnetic field are real is that they do not activate photon detectors. In order to met this objection I study several models of photon counter compatible with the reality of the fluctuations. The models predict a nonlinear dependence of the counting rate with the light intensity and the existence of a nonthermal dark rate, results which might explain the difficulty for performing loophole-free optical tests of Bell's inequality.

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arXiv2002

What is entanglement?

I conjecture that only those states of light whose Wigner function is positive are real states, and give arguments suggesting that this is not a serious restriction. Hence it follows that the Wigner formalism in quantum optics is capable of interpretation as a classical wave field with the addition of a zeropoint contribution. Thus entanglement between pairs of photons with a common origin occurs because the two light signals have amplitudes and phases, both below and above the zeropoint intensity level, which are correlated with each other.

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arXiv2002

A Local Hidden Variables Model for Experiments involving Photon Pairs Produced in Parametric Down Conversion

In previous articles we have developed a theory of down conversion in nonlinear crystals, based on the Wigner representation of the radiation field. Taking advantage of the fact that the Wigner function is always positive in parametric down conversion experiments, we construct a local hidden variables model where the amplitudes of the field modes are taken as random variables whose probability distribution is the Wigner function. In order to achieve our goal we give a model of detection which is fully local but departs from quantum theory. In our model the zeropoint (vacuum) level of radiation lies below a threshold of the detectors and only signals above the threshold are detectable. The predictions of the model agree with those of quantum mechanics if the signal intensities surpase some level and the efficiency is low. This is consistent with the known fact that quantum mechanics is compatible with local realism in that case (a fact called the ``efficiency loophole''). Our model gives a number of constraints which do not follow from the quantum theory of detection and are experimentally testable.

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arXiv2001

Quantum mechanics vs. local realism, is that the question?

The conjecture is made that quantum mechanics is compatible with local hidden variables (or local realism). The conjecture seems to be ruled out by the theoretical argument of Bell, but it is supported by the empirical fact that nobody has been able to perform a loophole-free test of local realism in spite of renewed effort during almost 40 years.

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arXiv2001

Local Realistic Theory for PDC Experiments Based on the Wigner Formalism

In this article we present a local hidden variables model for all experiments involving photon pairs produced in parametric down conversion, based on the Wigner representation of the radiation field. A modification of the standard quantum theory of detection is made in order to give a local realist explanation of the counting rates in photodetectors. This model involves the existence of a real zeropoint field, such that the vacumm level of radiation lies below the threshold of the detectors.

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arXiv1999

Irrelevance of photon events distinguishability in a class of Bell experiments

We show that the possibility of distinguishing between single and two photon detection events, usually not met in the actual experiments, is not a necessary requirement for the proof that the experiments of Alley and Shih [Phys. Rev. Lett. 61, 2921 (1988)], and Ou and Mandel [Phys. Rev. Lett. 61, 50 (1988)], are modulo fair sampling assumption, valid tests of local realism. We also give the critical parameters for the experiments to be unconditional tests of local realism, and show that some other interesting phenomena (involving bosonic type particle indistinguishability) can be observed during such tests.

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arXiv1997

The myth of the photon

We have shown that all "single-photon" and "photon-pair" states, produced in atomic transitions, and in parametric down conversion by nonlinear optical crystals, may be represented by positive Wigner densities of the relevant sets of mode amplitudes. The light fields of all such states are represented as a real probability ensemble (not a pseudoensemble) of solutions of the unquantized Maxwell equation. The local realist analysis of light-detection events in spatially separated detectors requires a theory of detection which goes beyond the currently fashionable single-mode photon theory. It also requires us to recognize that there is a payoff between detector efficiency and signal-noise discrimination. Using such a theory, we have demonstrated that all experimental data, both in atomic cascades and in parametric down conversions, have a consistent local realist explanation based on the unquantized Maxwell field. Finally we discuss current attempts to demonstrate Schroedinger-cat-like behaviour of microwave cavities interacting with Rydberg atoms. Here also we demonstrate that there is no experimental evidence which cannot be described by the unquantized Maxwell field. We conclude that misuse of the Photon Concept has resulted in a mistaken recognition of "nonlocal" phenomena.

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