arXiv subjects

Alejandro A. Hnilo

Publications and source records attributed to Alejandro A. Hnilo.

13 recordsLinked to original sources

arXiv2026

Einstein's 1927 gedanken experiment: how to complete it and measure the collapse time of a spatially spread photon

In the famous Solvay 1927 conference, Einstein discussed a gedanken experiment involving a single photon diffracted at an aperture and impinging on a screen. He devised the example to support De Broglie's hypothesis of the pilot wave, and his own ideas on the incompleteness of the description of physical reality provided by Quantum Mechanics. Partial realizations of Einstein's example have been performed, but the complete experiment has not been attempted (for good practical reasons) yet. Here I describe how to do it with accessible means. The setup will make possible to test Hellwig and Kraus postulate of covariant reduction of the quantum state.

quant-ph↗

arXiv2026

Quantum nonlocality: no, yes, how and why

The problem of the existence of nonlocal effects in Quantum Mechanics is discussed. The problem is divided in two: the first ('soft') one is to explain the violation of Bell's inequalities as a statistical magnitude. This can be achieved by a simple model within non-Boolean Locality and Realism. This result shows that quantum non-Locality as a consequence of the statistical violation of Bell's inequalities is inexistent. The second ('hard') problem is to explain the violation as it is calculated from series of detection outcomes. L.Sica has demonstrated that, in order to violate Bell's inequalities, the series recorded at (say) Bob when the setting at station Alice is alfa, can be different from the series that would have been recorded at Bob if that setting had been alfa'instead. Therefore, non-Locality in the series of detection outcomes does exist. It cannot be experimentally verified because of its counterfactual nature, but is observed in computer simulations. An appropriate computer code is based on the simple model mentioned plus a contextual instruction. It explains 'how' (Sica's) non-Locality arises, and solves the hard problem. 'Why' the contextual instruction exists is explained by Hellwig and Kraus' postulate of covariant quantum state collapse. In consequence, (Sica's) non-Locality is not in contradiction with Relativity but, quite the opposite, it is implied by Relativistic covariance.

quant-ph↗

arXiv2023

Is a spectrograph of hidden variables possible?

A new definition of "Realism" is proposed: it is that a gedanken "spectrograph" of hidden variables behaves as an actual (say, wavelength) spectrograph. The question is: does this definition allow, by itself, the derivation of Bell's inequalities? If it were, then such a spectrograph would be impossible, for Bell's inequalities are observed to be violated. In this short paper it is reported that, on the contrary, such spectrograph is compatible with the violation of Bell's inequalities. This result puts some new light on the controversy about the hypotheses necessary to derive Bell's inequalities. In particular, "Spectrograph's Realism", and "Locality", are proven to be different, and both necessary, hypotheses to derive Bell's inequalities.

quant-ph↗

arXiv2019

Measuring algorithmic complexity in chaotic lasers

Thanks to the simplicity and robustness of its calculation methods, algorithmic (or Kolmogorov) complexity appears as a useful tool to reveal chaotic dynamics when experimental time series are too short and noisy to apply Takens' reconstruction theorem. We measure the complexity in chaotic regimes, with and without extreme events (sometimes called optical rogue waves), of three different all-solid-state lasers: Kerr lens mode locking femtosecond Ti: Sapphire ("fast" saturable absorber), Nd:YVO4 + Cr:YAG ("slow" saturable absorber) and Nd:YVO4 with modulated losses. We discuss how complexity characterizes the dynamics in an understandable way in all cases, and how it provides a correction factor to the horizon of predictability given by Lyapunov exponents. This approach may be especially convenient to implement schemes of chaos control in real time.

physics.optics↗

arXiv2018

Addendum to: Kolmogorov complexity of sequences of random numbers generated in Bell's experiments (series of outcomes)

In the mentioned paper we presented results of the estimation of Kolmogorov complexity of sequences of random numbers generated in a famous Bell's experiment, aimed to study the security of QKD. We focused on series of time differences between successive detections of coincidences, and found that randomness cannot be taken for granted. It was then criticized that the theorems that demonstrate the randomness of series produced in Bell's experiments involve series of measurement outcomes, not of measurement times. Here we reply to this objection and present data of series of outcomes, showing that the conclusions in the mentioned paper are valid also in this case.

quant-ph↗

arXiv2018

On a different expression of the classical limit of quantum mechanics

The principle of correspondence (or classical limit) is essential in quantum mechanics. Yet, how and why quantum phenomena vanish at the macroscopic scale are issues still open to debate. Here, quantum mechanical predictions for Greenberger-Horne-Zeilinger states of qubits are shown to be easier to reproduce with a classical model as the number of particles increases, even in the absence of loopholes or conspiratorial mechanisms of any kind. It is conjectured that this result may lead to the simplest way to express the principle of correspondence.

quant-ph↗

arXiv2018

Kolmogorov complexity of sequences of random numbers generated in Bell's experiments

Quantum systems are the ultimate touchstone for the production of random sequences of numbers. Spatially spread entangled systems allow the generation of identical random sequences in remote locations. The impossibility of observing a quantum system, without disturbing it, ensures that the messages encoded using these sequences cannot be eavesdropped. This is the basis of Quantum Key Distribution. It is then of crucial importance knowing whether the sequences generated in the practice by spatially spread entangled states are truly random, or not. Yet, that knowledge is not immediate. One of the obstacles is the very definition of randomness. Statistical randomness is related with the frequency of occurrence of strings of data. On the other hand, algorithmic randomness is related with the compressibility of the sequence, what is given by Kolmogorov complexity. We analyze sequences generated by entangled pairs of photons focusing on an estimation of their complexity.

quant-ph↗

arXiv2015

Features of the extreme events observed in the all-solid state laser with a saturable absorber

Extreme events (sometimes also called optical rogue waves), in the form of pulses of extraordinary intensity, are easily observed in its chaotic regime if the Fresnel number of the cavity is high. This result suggests that the nonlinear interaction among transverse modes is an essential ingredient in the formation of extreme events in this type of lasers, but there is no theoretical description of the phenomenon yet. We report here a set of experimental results on the regularities of these extreme events, to provide a basis for the development of such a description. Among these results, we point out here: i) the decay of the correlation across the transversal section of the laser beam, and ii) the appearance of extreme events even if the time elapsed since the previous pulse is relatively short (in terms of the average inter-pulse separation), what indicates the existence of some unknown mechanism of energy storage. We hypothesize that this mechanism is related with the imperfect depletion of the gain by some of the transversal modes. We also present evidence in support of this hypothesis.

physics.optics↗

arXiv2014

On the features of the Optical Rogue Waves observed in the Kerr lens mode locked Ti:Sapphire laser

Kerr lens-mode-locked Ti:Sapphire lasers are known to display three coexistent modes of operation, that can be described as: continuous wave (CW), transform limited pulses (P1) and positive chirped pulses (P2). Optical rogue waves, in the form of pulses of high energy appearing much often than expected in a Gaussian distribution, are observed in the chaotic regime of the mode P2, but not of P1. These high energy pulses appear in an unpredictable way, but it is observed that their separation (if measured in number of round trips) can take only some definite values, which received the name of "magic numbers". The existence of optical rogue waves in P2 and not in P1, and also of the magic numbers, are correctly reproduced by a numerical simulation based on a five-variables iterative map. But, a successful numerical simulation provides limited insight on the physical causes of the observed phenomena. We present evidence that optical rogue waves in this laser follow a modulational instability, and that an initial condition in P1 rapidly evolves into P2 if the parameters' values are beyond that instability's threshold. The magic numbers are residuals of the periodic orbits of the "cold" cavity when it is perturbed by the opposite effects of a dissipative term, due to the presence of transversal apertures, and an expansive term, due to the Kerr effect.

physics.optics↗

arXiv2014

Time weakens the Bell's inequalities

By taking into account that all real measurements are performed successively, during time, it is concluded that the violation of the Bell's inequalities in the Nature does not refute (even in an ideally perfect experiment) the theories holding to Local Realism, for an unavoidable additional assumption is involved. Yet, in order to be acceptable, such theories must predict different values for the factual and counterfactual time averages of probabilities or observables.

quant-ph↗

arXiv2014

On the meaning of an additional hypothesis in the Bell's inequalities

The Bell's inequalities are derived from the hypotheses of Locality, Realism and (what is lesser known) the equality between the factual and the counterfactual time averages of the expectation values of observables. The necessity of a hypothesis additional to Local Realism opens a promising way out to the old controversy between Quantum Mechanics and Local Realism. For, it is possible to speculate that it is this additional hypothesis, and not Local Realism, what is disproved in the experiments reporting the violation of the Bell's inequalities. Yet, there are doubts on how the additional hypothesis may be violated in a physically reasonable process. A simple example showing that this is possible, the relationship between the validity of the additional hypothesis and the validity of the Bell's inequalities, and considerations on its physical meaning, are presented.

quant-ph↗

arXiv2013

Measuring entanglement of photons produced by a pulsed source

A pulsed source of entangled photons is desirable for some applications. Yet, such a source has intrinsic problems arising from the simultaneous arrival of the signal and noise photons to the detectors. These problems are analyzed and practical methods to calculate the number of accidental (or spurious) coincidences are described in detail, and experimentally checked, for the different regimes of interest. The results are useful not only to measure entanglement, but to all the situations where extracting the number of valid coincidences from noisy data is required. As an example of the use of those methods, we present the time-resolved measurement of the Concurrence of the field produced by spontaneous parametric down conversion with pump pulses of duration in the ns-range at a repetition of kHz. The predicted discontinuous evolution of the entanglement at the edges of the pump pulse is observed.

physics.optics↗

arXiv2012

Observable consequences of a hypothetical transient deviation from Quantum Mechanics

The conflict between Quantum Mechanics (QM) and the intuitive concepts of Locality and Realism (LR) is manifest in the correlation between measurements performed in remote regions of a spatially spread entangled state. In this paper, it is hypothesized that transient deviations (from the values predicted by QM) occur if the correlation is measured in a time shorter than L/c, where L is the spatial spread of the entangled state and c is the speed of light. In this way, the conflict is solved by changing QM minimally. Under general assumptions, it is obtained a mathematical model of the process that reproduces the QM value after a time longer than L/c has elapsed. One of the predictions of this model is that oscillations of the rate of coincidences should exist, with a main frequency lower than c/4L. An experiment able to reveal these oscillations is shown to be accessible, by placing stations at about 5 Km and reaching a coincidence rate about 3E5 1/s (a value already obtained at the laboratory scale). This means a test of QM vs LR of a completely new type, with several practical and theoretical advantages.

quant-ph↗