arXiv subjects

Alejandro Hnilo

Publications and source records attributed to Alejandro Hnilo.

At least 19 recordsLinked to original sources

arXiv2026

Test of the essential collapse-locality loophole

Collapse-locality is an untested loophole in the violation of Bell's inequalities. The core of the argument is that the time value of photon detection is delayed by the time Tc required by the collapse of its quantum state. The value of Tc is given by the underlying theory of quantum collapse, and is mostly unknown. Depending on the value of Tc, detections in the performed Bell's experiments may have not been truly space-like separated events. This implies that the inequalities may have been violated as a consequence of (conspiratorial) information propagating at subluminal speed. We report an optical Bell experiment which closes the weaker ('essential') form of this loophole regardless the theory of quantum collapse. This is possible thanks to unique features of the setup. These features are: classical signals sent to the stations to define a time reference, and variable distance between the stations leaving all other parameters constant.

quant-ph↗

arXiv2025

Quantum mysteries explained in digestible form

Years ago, Itamar Pitowski asked two relevant questions: Why microphysical (quantum) phenomena and classical phenomena differ in the way they do? and, what kind of explanation could qualify as a reasonable one? I argue that both questions can be answered by the comparison of quantum phenomena with some features of vectors in real space. In particular, I show how violation of Bell's inequalities, Teleportation, Kochen-Specker and Greenberger-Horne-Zeilinger theorems can be understood in terms of vectors. This does not mean that the difference between quantum and classical phenomena is illusory. This means that vectors are stranger objects that they may seem to be at first sight.

quant-ph↗

arXiv2025

Experiment indicates that Realism, not Locality, is false in Quantum Mechanics

The interpretation of the meaning of Quantum Mechanics has faced controversy since its inception. Bell's inequalities are a touchstone in this controversy. Their observed violation demonstrates that at least one of the hypotheses involved in their derivation and test is false in Nature. In principle, one has to choose between accepting that Locality is false, what implies a possible contradiction with the Theory of Relativity, or accepting that Realism is false, what means to give up the existence of a physical world independent of the observer. The right answer has consequences both foundational and practical, and theoretical discussions have searched it for decades. We report the results of a Bell's experiment designed and performed to add observational information to the discussion. Three proposals to reveal the false hypothesis are carried out, namely: search of attractors in time series of observations, variation of randomness of binary series of outcomes between space-like and not-space-like separated conditions of observation, and test of a bound of Kolmogorov's complexity. The results are consistent with the absence of the specific form of Realism usually involved in the derivation of Bell's inequalities, while remaining compatible with Locality within the sensitivity of the tests. Independently of the foundational problem and of any interpretation, some bare observations have immediate practical impact on the best use of device-independent quantum Random Number Generators and Quantum Key Distribution.

quant-ph↗

arXiv2024

Kochen-Specker for many qubits and the classical limit

Several arguments demonstrate the incompatibility between Quantum Mechanics and classical Physics. Bell's inequalities and Greenberger-Horne-Zeilinger (GHZ) arguments apply to specific non-classical states. The Kochen-Specker (KS) one, instead, is especially appealing for it applies to any state. Nevertheless, in spite of the incompatibility, quantum predictions must converge to classical ones as the macroscopic scale is approached. This convergence is known as "classical limit", and is difficult to explain within quantum formalism. In this short paper, the simplified Mermin-Peres form (two qubits) of the KS argument is extended to an arbitrary number of qubits. It is shown that quantum and classical predictions converge as the number of qubits is increases to the macroscopic scale. This way to explain the classical limit concurs with, and improves, a result previously reported for GHZ states. The demonstration for the general case (i.e., for all possible observables) that the classical limit is the consequence of merely increasing the number of particles, is important and seems to be at hand.

quant-ph↗

arXiv2024

Time series and the meaning of quantum non-locality

Quantum non-locality has become a popular term. Yet, its precise meaning, and even its mere existence, is the subject of controversies. The main cause of the controversies is the never ending discussion on the appropriate definitions of Locality and Realism in the derivation of Bell's inequalities. On the other hand, Louis Sica derived Bell's inequalities from the hypothesis that time series of outcomes observed in one station do not change if the setting in the other (distant) station is changed. The derivation is based on arithmetical properties of time series only; it does not involve the definitions of Locality, Realism and probabilities, and is valid for series of any length. An important consequence is that violation of Bell's inequalities implies the series recorded (at the same time) in one station to be different if the setting in the other station is changed. This result gives precise meaning to the idea of quantum non-locality, and also makes evident why using it for faster than light signaling is impossible (because the difference is between factual and counter-factual series). Finally, it is demonstrated that series of outcomes, even if they violate Bell's inequalities, can be always embedded in a set of factual and counter-factual data that does hold to Bell's inequalities. Loosely speaking, the factual world may be quantum or not, but the union of factual and counter-factual worlds is always classical.

quant-ph↗

arXiv2024

Proposal of an optical Bell's experiment to test the boundary between determinism and indeterminism in Quantum Mechanics

It was recently noted the existence of an apparently discontinuous boundary between determinism and indeterminism in Quantum Mechanics. We propose to explore this boundary in an optical Bell's experiment by recording the distribution, of the number of strings of outcomes of a given parity interrupted by outcomes of the other parity, as a function of their length. The features of these distributions for small rotations of the angle settings near critical points may indicate whether the underlying process is in-deterministic or not. Therefore, they may show that the boundary is discontinuous, or else, that determinism decays smoothly. The conditions the experimental setup must fulfill are discussed.

quant-ph↗

arXiv2024

Test of transient deviations from Quantum Mechanics in Bell's experiment

The conflict between Quantum Mechanics (QM) and Local Realism is most noticeable in the correlations observed between distant regions of a spatially spread entangled state. It has been hypothesized that transient deviations (from the values predicted by QM) may be observed if the correlations are 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. This hypothesis is appealing for it solves that conflict by minimally modifying the interpretation of QM, and opens the door to potentially fruitful nonlinear generalizations of QM without the risk of allowing faster-than-light signaling. The hypothesis is technically impossible to test directly nowadays, but a stroboscopic test is attainable. We present the results of such a test performed on a specially designed optical Bell setup with a distance between stations up to 24 m in straight line. No difference with the same observations performed at short distance, or evidence of transient deviations, is found. Yet, several hypotheses are involved in this experiment; they are detailed and briefly discussed. To say the least, the space left for the hypothesis of transient deviations is much reduced.

quant-ph↗

arXiv2024

Machine learning predicts extreme events in ultrashort pulse lasers

In this paper we present a nonlinear autoregressive neural network with a hidden layer of 50 neurons, three delays and one output layer that accurately is capable of predict the appearence of extreme events in a Kerr lens mode locking Ti:Sapphire laser with ultrashort pulses. Extreme events are produced in the context of a chaotic atractor and with chirped pulses. The prediction of this neural network works well with experimental and theoretical time series of amplitude of laser pulses. When fed with experimental time series we have 95.45\% of hits and 6.67\% of false positives while using theoretical time series the network predicts 100\% of extreme events but the false positive rise to 23.33\%.

physics.optics↗

arXiv2023

The distinctive symmetry of Bell states

The Bell's basis is composed of four maximally entangled states of two qubits, named Bell states. They are usual tools in many theoretical studies and experiments. The aim of this paper is to find out the symmetries that determine a Bell state. For this purpose, starting from a general density matrix, physical constraints and symmetry conditions are added until the elements of the Bell's basis are univocally determined. It is found that the usual physical constraints and symmetry conditions do not suffice to determine a Bell state. The additional restriction needed is named here atomic symmetry. It is a sort of global symmetry of the system, not derived from the action = reaction law. It is also found that the imperfection in fulfilling the atomic symmetry is linearly proportional to the deviation of the Concurrence from its maximum value. The atomic symmetry allows a different insight on the nature of entanglement, and might be useful as a criterion to define the condition of maximal entanglement for states with more than two qubits.

quant-ph↗

arXiv2023

'Frequency-modulated' pulsed Bell setup avoids post-selection

Excepting event-ready setups, Bell experiments require post-selection of data to define coincidences. From the fundamental point of view, post-selection is a true 'logical loophole'. From the practical point of view, it implies a numerically heavy and time consuming task. In Quantum Key Distribution (QKD), it opens vulnerability in case of a hostile adversary. The core of the problem is to synchronize independent clocks during long observation runs. A pulsed source gets rid of clocks' drift, but there is still the problem of identifying the same pulse in each remote station. We use a frequency modulated pulsed source to achieve it. This immediately defines the condition of valid coincidences in a manner that is unaffected by the drift between the clocks. It allows finding the set of entangled pairs avoiding post-selection and in a way that is found to be optimal. It is also robust against a hostile adversary in the case of QKD.

quant-ph↗

arXiv2022

Testing randomness of series generated in Bell's experiment

The generation of series of random numbers is an important and difficult problem. Even the very definition of random is difficult. Appropriate measurements on entangled states have been proposed as the definitive solution to produce series of certified randomness. However, several reports indicate that quantum based devices show a disappointing rate of series rejected by standard tests of randomness. This problem is usually solved by using algorithms named extractors but, if the extractor were known by an eavesdropper (a situation that cannot be ruled out) the key security in QKD setups may be menaced. We use a toy fiber optic based setup, similar to a QKD one to be used in the field, to generate binary series, and evaluate their level of randomness according to Ville principle. Series are tested with a battery of standard statistical indicators, Hurst exponent, Kolmogorov complexity, minimum entropy, Takens dimension of embedding, and Augmented Dickey Fuller and Kwiatkowski Phillips Schmidt Shin to check stationarity. A theoretically predicted relationship between complexity and minimum entropy is observed. The good performance of a simple method to get useful series from rejected series, reported by Solis et al, is confirmed and supported with additional arguments. Regarding QKD, the level of randomness of series obtained by applying Toeplitz extractor to rejected series is found to be indistinguishable from the level of non-rejected raw ones.

quant-ph↗

arXiv2021

About the description of physical reality of Bell's experiment

A hidden variables model complying with the simplest form of Local Realism was recently introduced, which reproduces Quantum Mechanics' predictions for an even ideally perfect Bell's experiment. This is possible thanks to the use of a non-Boolean vector hidden variable. Yet, that model is as far as Quantum Mechanics from the goal of providing a complete description of physical reality in the EPR-sense. Such complete description includes the capacity to calculate, from the values taken by the hidden variables, the time values when particles are detected. This can be achieved by replacing Born's rule (which allow calculating only probabilities) with a deterministic condition for particle detection. The simplest choice is a threshold condition on the hidden variables. However, in order to test this choice, a new type of quantum (or wave, or non-Boolean) computer is necessary. This new type of quantum computer does not exist yet, not even in theory. In this paper, a classical (Boolean) computer code is presented which mimics the operation of that new type of quantum computer by using contextual instructions. These instructions take into account a consequence of the principle of superposition (which is a typical vector, i.e. non-Boolean, feature). Numerical results generated by the mimicking code are analyzed. They illustrate the features the hypothetical new type of quantum computer's output may have, and show how and why some intuitive assumptions about Bell's experiment fail.

physics.gen-ph↗

arXiv2020

LIGO series, dimension of embedding and Kolmogorov's complexity

The interpretation of the series recorded by the Laser Interferometer Gravitational Wave Observatory is a very important issue. Naturally, it is not free of controversy. Here we apply two methods widely used in the study of nonlinear dynamical systems, namely, the calculation of Takens' dimension of embedding and the spectrum of Kolmogorov's complexity, to the series recorded in event GW150914. An increase of the former and a drop of the latter are observed, consistent with the claimed appearance of a gravitational wave. We propose these methods as additional tools to help identifying signals of cosmological interest.

astro-ph.IM↗

arXiv2020

Non-Boolean Hidden Variables model reproduces Quantum Mechanics' predictions for Bell's experiment

The experimentally verified violation of Bell's inequalities apparently implies that at least one of two intuitive beliefs must be false: that effects propagating at infinite velocity do not exist, and that natural phenomena occur independently of being observed. Giving up any one of these two beliefs (usually known together as Local Realism) is controversial. Many theories have been proposed to reconcile the violation of Bell's inequalities with Local Realism, but none has been fully successful. In this paper, it is recalled that any theory aimed to violate Bell's inequalities must start by giving up Boolean logic. The problem is split in two: the "soft" problem is to explain the violation of Bell's inequalities within (non-Boolean) Local Realism. The "hard" problem is to predict the time values when single particles are detected. A simple hidden variables model is introduced, which solves the soft problem. This is possible thanks to the use of vectors as the hidden variables and the operation projection, which do not hold to Boolean logic. This model reconciles the violation of Bell's inequalities with Local Realism and should end decades of controversy. Regarding the hard problem, the introduced model is as incomplete as Quantum Mechanics is. It is argued that solving the hard problem involves devising a new kind of quantum computer, which should be able to accept (non-Boolean) hidden variables as input data and replace the statistical Born's rule with a deterministic threshold condition.

quant-ph↗

arXiv2020

Quantum Mechanical description of Bell's experiment assumes Locality

Here it is shown that the simplest description of Bell's experiment according to the canon of von Neumann's theory of measurement explicitly assumes the (Quantum Mechanics-language equivalent of the classical) condition of Locality. This result is complementary to a recently published one demonstrating that non-Locality is necessary to describe said experiment within the framework of classical hidden variables theories, but that it is unnecessary to describe it within the framework of Quantum Mechanics. Summing up these and other related results, it is concluded that, within the framework of Quantum Mechanics, there is absolutely no reason to believe in the existence of non-Local effects. In addition to its foundational significance, this conclusion has practical impact in the fields of quantum-certified and device-independent randomness generation and on the security of Quantum Key Distribution schemes using entangled states.

quant-ph↗

arXiv2020

Using Randomness to decide among Locality, Realism and Ergodicity

Loophole-free experiments have demonstrated that at least one of three features is false when the violation of Bell's inequalities is observed: Locality, Realism or (what is lesser known) Ergodicity. An experiment is proposed to find out, or at least to get an indication about, which one is false. It is based on recording the time evolution of the rate of series of outcomes that are found not-random in a pulsed Bell's setup. The results of such experiment would be important not only to the foundations of Quantum Mechanics. For, even if the foundational issue remained not fully decided, they would have immediate practical impact on the efficient use of quantum-certified Random Number Generators and the security of Quantum Key Distribution using entangled states.

quant-ph↗

arXiv2019

Randomness of imperfectly entangled states

The generation of series of random numbers is an important and difficult problem. Appropriate measurements on entangled states have been proposed as the definitive solution, based on the impossibility of exploiting quantum non locality to get faster than light signaling. There is a controversy regarding what is preferable to produce series with utilizable randomness in practice, high or low entanglement. We prepare biphotons with three different levels of entanglement, easy entangled, marginally entangled and no entangled. Randomness is evaluated, independently of the quantum non locality argument, through a battery of standard statistical tests, Hurst exponent, Kolmogorov complexity, Takens dimension of embedding, and Augmented Dickey Fuller and Kwiatkowski Phillips Schmidt Shin tests to check stationarity. The no entangled case is found to produce the smallest rate of not random series, and the marginal case the largest. Although the entangled case has a larger rate of not random series than the no entangled case, it is found still acceptable for QKD.

quant-ph↗

arXiv2017

Extreme Events related with spatial patterns in an all-solid-state laser with saturable absorber

The passively Q-switched, self-pulsing all-solid-state laser is a device of widespread use in many applications. Depending on the condition of saturation, which is easy to adjust, different dynamical phenomena are observed: continuous wave emission, stable oscillations, period doubling bifurcations, chaos and, in some chaotic regimes, extreme events in the form of pulses of extraordinary intensity. These pulses are also sometimes called "dissipative optical rogue waves". The mechanism of their formation is still unknown. Here, we report the direct observation of the pulse-to-pulse evolution of the transverse pattern with an ultrafast camera (up to 60,000 frames per second). A specific pattern is correlated with the pulse intensity in the periodical regimes. In the chaotic regimes, the extreme events are correlated with some patterns. The series of patterns before and after an extreme event are often the same. These observations demonstrate that extreme events in this system are the consequence of the deterministic nonlinear interaction of few modes. This information plays a crucial role in the development of a theoretical model able to describe the mechanism giving raise to extreme events. The model is expected to lead to the control of their formation at will, what is of practical interest.

physics.optics↗