Person: Luis Aina, Alfredo
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First Name
Alfredo
Last Name
Luis Aina
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Óptica
Area
Optica
Identifiers
112 results
Search Results
Now showing 1 - 10 of 112
Item Nonlinear Michelson interferometer for improved quantum metrology(Physical review A, 2015) Luis Aina, Alfredo; Rivas Vargas, ÁngelWe examine quantum detection via a Michelson interferometer embedded in a gas with Kerr nonlinearity. This nonlinear interferometer is illuminated by pulses of classical light. This strategy combines the robustness against practical imperfections of classical light with the improvement provided by nonlinear processes. Regarding ultimate quantum limits, we stress that, as a difference with linear schemes, the nonlinearity introduces pulse duration as a new variable into play along with the energy resources.Item Nonclassicality in phase by breaking classical bounds on statistics(Physical review A, 2010) Martín, Daniel; Luis Aina, AlfredoWe derive upper bounds on the statistics of phase and phase difference that are satisfied by all classical states. They are obtained by finding the maximum projection of classical states on phase states. For a single-mode phase, meaningful bounds are obtained conditioned to a fixed mean number of photons. We also derive classical bounds for the projection on phase-coherent states, discussing their relation with phase-state bounds within the context of analytic representations. We find states with nonclassical phase properties disclosed by the violation of these classical bounds. These are quadrature and SU(2) squeezed states and phase-coherent states.Item SU(2)-invariant depolarization of quantum states of light(Physical review A, 2013) Rivas Vargas, Ángel; Luis Aina, AlfredoWe develop an SU(2)-invariant approach to the depolarization of quantum systems as the effect of random unitary SU(2) transformations. From it we derive an SU(2)-invariant Markovian master equation. This is applied to several quantum states examining whether nonclassical states are more sensible to depolarization than the classical ones. Furthermore, we show that this depolarization model provides a nontrivial generalization of depolarization channels to states of arbitrary dimension.Item Classical and quantum complementarity(Physics letters A, 2020) Galazo, Raquel; Bartolomé, Irene; Ares Santos, Laura; Luis Aina, AlfredoTwo complementary observables can be measured simultaneously so that the exact individual distributions can be recovered by a proper data inversion. We apply this program to the paradigmatic example of the Young interferometer from the classical and quantum points of view. We show complete parallelism between complementarity in the quantum and classical theories. In both domains, complementarity manifests in a pathological behavior for the inferred joint distribution. (C) 2020 Elsevier B.V. All rights reserved.Item Probability distributions for the phase difference(Physical review A, 1996) Luis Aina, Alfredo; Sánchez Soto, Luis LorenzoIn this work we analyze the quantum phase properties of pairs of electromagnetic field modes. Since phases differing by 2π are physically indistinguishable, we propose a general procedure to obtain the correct mod(2π) probability distributions for the phase difference. This allows us to investigate the properties of a number of phase approaches. This procedure provides deeper insight into the quantum nature of the phase difference. We relate this problem to the representation of nonbijective canonical transformations in quantum mechanics.Item Nonclassicality in weak measurements(Physical review A, 2004) Johansen, Lars M.; Luis Aina, AlfredoWe examine weak measurements of arbitrary observables where the object is prepared in a mixed state and on which measurements with imperfect detectors are made. The weak value of an observable can be expressed as a conditional expectation value over an infinite class of different generalized Kirkwood quasiprobability distributions. "Strange" weak values for which the real part exceeds the eigenvalue spectrum of the observable can only be found if the Terletsky-Margenau-Hill distribution is negative or, equivalently, if the real part of the weak value of the density operator is negative. We find that a classical model of a weak measurement exists whenever the Terletsky-Margenau-Hill representation of the observable equals the classical representation of the observable and the Terletsky-Margenau-Hill distribution is non-negative. Strange weak values alone are not sufficient to obtain a contradiction with classical models. We propose feasible weak measurements of photon number of the radiation field. Negative weak values of energy contradict all classical stochastic models, whereas negative weak values of photon number contradict all classical stochastic models where the energy is bounded from below by the zero-point energy. We examine coherent states in particular and find negative weak values with probabilities of 16% for kinetic energy (or squared field quadrature), 8% for harmonic oscillator energy, and 50% for photon number. These experiments are robust against detector inefficiency and thermal noise.Item Complementarity for generalized observables(Physical review letters, 2002) Luis Aina, AlfredoWe examine basic properties of complementarity by using the most general description of quantum observables as positive-operator measures. We show that, in general, two observables can be complementary or not depending on the measure of fluctuations adopted and that complementarity is not a symmetric relation. This occurs because the states that determine the measured statistics do not necessarily coincide with the minimum uncertainty states for the same observable. We also show that there are observables without a complementary observable and that complementarity is not preserved by the Neumark extensions.Item Coherence versus interferometric resolution(Physical review A, 2010) Luis Aina, AlfredoWe examine the relation between second-order coherence and resolution in the interferometric detection of phase shifts. While for classical thermal light resolution and second-order coherence are synonymous, we show that for quantum light beams reaching optimum precision second-order coherence and resolution become antithetical.Item Reconciling quantum trajectories and stationary quantum distributions in single-photon polarization states(Physical review A, 2013) Luis Aina, Alfredo; Sanz, Ángel S.The question of the representation of quantum stationary partially polarized waves as random superpositions of different polarization ellipses is addressed. To this end, the Bohmian formulation of quantum mechanics is considered and extended to quantum optical polarization. As is shown, this approach properly combines definite time-evolving trajectories with rigorous stationary quantum distributions via the topology displayed by the associated phase field.Item Reply to ‘‘Comment on ‘Phase-difference operator’ ’’(Physical review A, 1995) Luis Aina, Alfredo; Sánchez Soto, Luis LorenzoIn response to the objection raised by Pegg and Vaccaro [the preceding Comment] we point out that their example is not a difhculty in directly representing the phase difference by the φ12 operator. In fact, we argue that it is a property common to a wide range of phase descriptions, including the Pegg-Barnett formalism.