arXiv subjects

Alfredo Luis

Publications and source records attributed to Alfredo Luis.

At least 19 recordsLinked to original sources

arXiv2026

Conditional probabilities in quantum-optical settings

We examine conditional probabilities derived from the joint noisy measurement of two complementary observables. We show that conditioning on one variable can lead to reduction of uncertainty in the other one, even completely eliminating uncertainty. We show that the conditional distribution cannot, in general, be represented in Born form using the marginal positive operator valued measure and any physical system state, nor can it be derived from typical rules of state reduction. We examine these issues in two basic quantum-optical schemes. These are double homodyne detection and a qubit measurement.

quant-ph↗

arXiv2026

Quantum tests via inequalities for joint statistics

In this work we derive statistical inequalities whose violation is equivalent to the impossibility of describing the data by a genuine joint probability distribution. So they are witnesses of the failure of a common probability space. We examine whether the most significant quantum quasidistributions violate these inequalities. We examine also whether these inequalitites are violated by the joint distributions derived form a noisy joint measurement. As a relevant example we find violations for the maximally mixed state, as well as cases where all system states violate them. This points to the idea that these results are more than a property of the system states, but are instead a property of the statistical structure of quantum mechanics.

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arXiv2026

Kirkwood-Dirac distributions in classical optics

We develop a comprehensive analysis of the Kirkwood-Dirac distributions in classical optics, revealing their deep connection with optical coherence as fundamental concept in optics. From their very definition, the Kirkwood-Dirac distributions emerge as generalized mutual coherence functions involving two different bases instead of just one. This perspective provides a unified interpretation of the so-called anomalous values, that are complex and negative values, as direct manifestations of coherence. We show that this interpretation consistently applies across all field variables considered in this work, including polarization, interference and wave propagation. Furthermore, we propose diverse methods of experimental determination of these distributions based on interference, in full agreement with their coherence-based interpretation.

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arXiv2025

Impact of quadrature measurement on quantum coherence

We examine the behavior of quadrature coherence under the measurement of the same field quadrature. This is carried out with the help of a beam splitter, which implies the contribution of an auxiliary field state impinging at the other input port. To this end we consider the linear input-output transformation of a lossless beam splitter to relate input and output coherences, measured in terms of the $l_1$-norm. After obtaining a general input-output relation between coherences we apply the result to Gaussian and number states. For Gaussian states we obtain that coherence does not depend on the measurement outcome, and that the average coherence always equals the coherence of the reduced state, showing no average effect on coherence of the measurement. On the other hand, for number states the output coherence depends on the measurement, decreasing the relative coherence with increasing photon number. Finally, we consider relative-entropy as a measure of coherence to show that for number states and coherence measures other than the $l_1$-norm the average coherence no longer equals the coherence of the output reduced state.

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arXiv2025

Generalized measurements for Bell tests in different probability spaces

Bell tests are of profound statistical nature. Besides physical considerations, the proper understanding of their implications should involve detailed statistical analyses. In this regard, recent works have shown that their consequences and interpretations depend on the probability space adopted. Some other recent works have also shown that generalized measurements may allow to further exploit the statistics of Bell-like tests. Following these ideas, in this work we show that one and the same experimental arrangement can provide a practical scheme valid for two very different probability spaces. Moreover, we show that this allows the introduction of novel Bell tests that are not possible in more standard approaches.

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arXiv2025

Statistical analysis of Bell tests via generalized measurements

We provide a fully statistical analysis of the results of a Bell test beyond mean values. This is possible in a practical scheme where all the observables involved in the test are simultaneously measured at the expense of unavoidably additional noise. To deal with this noise we can follow two strategies leading to the same results. These are to adapt the Bell bound to include the noise, or to remove the additional noise via suitable data inversion.

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arXiv2025

Single-measurement Bell analysis

We examine the satisfaction of Bell criteria for single realizations of quantum systems. This is possible via the joint noisy measurement of all observables involved in the Bell test.We readily find that every outcome violates Bell bounds for local hidden variables models. This agrees with the idea that to reveal nonclassical effects a necessary condition is that the measuring scheme itself must be nonclassical.

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arXiv2024

Eluding Zeno effect via dephasing and detuning

We analyze some variants of the Zeno effect in which the frequent observation of the population of an intermediate state does not prevent the transition of the system from the initial state to a certain final state. This is achieved by considering system observation involving suitably introduced phase shifts and detunings that leads to a rather rich measurement-induced dynamics by the alteration of the interference governing quantum evolution. For initial nonclassical states this includes entanglement as a way of evolution from the initial to the final state avoiding the intermediate state. This possibility is presented in a particular physical scenario in the form of a chain of three coupled harmonic oscillators, but we readily show then that the idea can be applied to other physical systems as well, such as atomic-level dynamics. These results are significant for a better knowledge of fundamental quantum concepts as well as regarding suitable applications in the proper control of quantum dynamics, as this is a key feature of modern applications of the quantum theory.

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arXiv2024

Photonic Entanglement and Polarization Nonclassicality: Two Manifestations, One Nature

We demonstrate in theory and experiment the strict equivalence between nonclassical polarization and the entanglement of indistinguishable photons, thereby unifying these two phenomena that appear dissimilar at first sight. This allows us to analyze nonclassicality and multi-photon entanglement within the same framework. We experimentally verify this double-sided form of quantumness and its independence from the polarization basis, contrasting other notions of coherence that are highly basis-dependent. Our findings show how nonclassical polarization turns out to be equally resourceful for quantum protocols as entanglement, emphasizing its importance in practical applications.

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arXiv2024

Coherence via reiterated beam splitting

Beam splitters are not-free operations with regard to quantum coherence. As a consequence, they can create coherence from both coherent and incoherent states. We investigate the increase in coherence produced by cascades of beam splitters. To this end, we construct two different configurations and analyze different sequences of input states.

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arXiv2024

Spatial and temporal coherence via polarization mutual coherence function

We address polarization coherence in terms of correlations of Stokes variables. We develop an scalar polarization mutual coherence function that allows us to define a polarization coherence time. We find a suitable spectral polarization density allowing a polarization version of the Wiener-Khintchine theorem. With these tools we also address the polarization version of the van Cittert-Zernike theorem.

physics.optics↗

arXiv2023

Coherence and incoherence in quadrature basis

How to manage coherence as a continuous variable quantum resource is still an open question. We face this situation from the very definition of incoherent states in quadrature basis. We apply several measures of coherence for some physical states of light relative to a quadrature basis. We examine the action on the coherence of several transformations such as beam splittings and squeezing.

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arXiv2022

Phase-space quantum Wiener-Khintchine theorem

We derive a quantum version of the classical-optics Wiener-Khintchine theorem within the framework of detection of phase-space displacements with a suitably designed quantum ruler. A phase-pace based quantum mutual coherence function is introduced that includes the contribution of the detector. We obtain an universal equality linking resolution with coherence. This is illustrated with the case of Gaussian states and number states.

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arXiv2022

Quantum conditional probabilities

We investigate the consistency of conditional quantum probabilities. This is whether there is compatibility between the Kolmogorov-Bayes conditional probabilities and the Born rule. We show that they are not compatible in the sense that there are situations where there is no legitimate density matrix that may reproduce the conditional statistics of the other observable via the Born rule. This is to say that the Gleason theorem does not apply to conditional probabilities. Moreover, we show that when this occurs the joint statistics is nonclassical. We show that conditional probabilities are not equivalent to state reduction, so these results do not affect the validity of the Lüders expression.

quant-ph↗

arXiv2022

Beam splitter as quantum coherence-maker

The aim of this work is to answer the question of how much quantum coherence a beam splitter is able to produce. To this end we consider as the variables under study both the amount of coherence of the input states as well as the beam splitter characteristics. We conclude that there is an optimal combination of these factors making the gain of coherence maximum. In addition, the two mode squeezed vacuum arises as the studied state most capable of gaining coherence when passing through a beam splitter. These results are qualitatively equivalent for the the l1-norm of coherence and for the relative entropy of coherence.

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arXiv2022

Distance-based approach to quantum coherence and nonclassicality

We provide a coherence-based approach to nonclassical behavior by means of distance measures. We develop a quantitative relation between coherence and nonclassicality quantifiers, which establish the nonclassicality as the maximum quantum-coherence achievable. We compute the coherence of several representative examples and discuss whether the theory may be extended to reference observables with continuous spectra.

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arXiv2022

Inequalities for complementarity in observed statistics

We provide an analysis of complementarity via a suitably designed classicalmodel that leads to a set of inequalities that can be tested by means ofunsharp measurements. We show that, if the measured statistics does notfulfill the inequalities it is equivalent to the lack of a joint distribution for theincompatible observables. This is illustrated by path-interference duality ina Young interferometer.

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arXiv2021

Coherence, nonclassicality and metrological resolution

We demonstrate the simple and deep equivalence between quantum coherence and nonclassicality and the definite way in which they determine metrological resolution. Moreover, we define a coherence observable consistent with a classical intuition relating coherence with phase statistics.

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