Información del autor
Autor Luis Aina, Alfredo |
Documentos disponibles escritos por este autor (102)
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An alternative derivation of the Pegg-Barnett phase operator is presented. This approach is based on the properties of the representation in quantum mechanics of a nonlinear nonbijective canonical transformation. It does not use as its starting [...]texto impreso
We examine a family of intrinsic performance measures in terms of probability distributions that generalize Hellinger distance and Fisher information. They are applied to quantum metrology to assess the uncertainty in the detection of minute cha[...]texto impreso
We derive simple practical procedures revealing the quantum behavior of angular momentum variables by the violation of classical upper bounds on the statistics. Data analysis is minimum and definite conclusions are obtained without evaluation of[...]texto impreso
Two examples are presented where the observation of the emission in parametric down-conversion leads to its enhancement instead of its inhibition. The improvement is analyzed in terms of the quantum features of the observation.texto impreso
Any nonclassical effect noticed in measured statistics is usually attributed just to the light state being observed. According to Born's rule, quantum probabilities are given by the overlap between the system state and measurement states in a qu[...]texto impreso
We analyze the performance of nonlinear detection schemes surpassing the Heisenberg limit with semiclassical input states when using realistic detectors having nonunit detection efficiency.texto impreso
We provide a very simple case showing that the weak form of the Heisenberg limit can be beaten while the prior information is improved without bias.texto impreso
The well-known difficulties of defining a phase operator of an oscillator are considered from the point of view of the canonical transformation to action and phase-angle variables. This transformation turns out to be nonbijective, i.e., it is no[...]texto impreso
We elaborate an approach to quantum fluctuations of angular momentum based on the diagonalization of the covariance matrix in two versions: real symmetric and complex Hermitian. At difference with previous approaches this is SU(2) invariant and [...]texto impreso
Bermúdez, A. ; Martín-Delgado Alcántara, Miguel Ángel ; Luis Aina, Alfredo | American Physical Society | 2008-06-11We study a relativistic spin-1/2 fermion subjected to a Dirac oscillator coupling and a constant magnetic field. An interplay between opposed chirality interactions culminates in the appearance of a relativistic quantum phase transition, which c[...]texto impreso
Two 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[...]texto impreso
We compare the maximum achievable polarization correlations for classical-like separable states and quantum entangled states. For one-photon systems we find that the maximally entangled states have three times larger correlations than the maximu[...]texto impreso
Geometrical optics can be regarded both as the short-wavelength approximation of the propagation of electromagnetic waves, and as the exact way in which propagate the surfaces of discontinuity of the classical electromagnetic field. In this work[...]texto impreso
Porras, Miguel A. ; Luis Aina, Alfredo ; Gonzalo Fonrodona, Isabel | American Physical Society | 2013-11-04We provide theoretical and experimental evidence of a classical-optics realization of quantum Zeno dynamics. In contrast to other approaches, the classical implementation is extremely simple and adaptable. Frequently monitoring the transverse sp[...]texto impreso
Two-path interference of transversal vectorial waves is embedded within a larger scheme: this is four-path interference between four scalar waves. This comprises previous approaches to coherence between vectorial waves and restores the equivalen[...]texto impreso
We 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 [...]texto impreso
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Very simple duality relations-assessing complementarity for two-dimensional systems are obtained by introducing a measure of fluctuations derived from dispersion. These relations fully explain the enforcement of complementarity in situations in [...]texto impreso
We generalize to systems with arbitrary finite dimension a measure of quantum fluctuations (the certainty) previously introduced for two-dimensional systems. Using this measure, we study the duality relations satisfied by complementary observabl[...]texto impreso
Quantum phase difference is used to analyze which-path detectors in which the loss of interference predicted by complementarity cannot be attributed to classical momentum transfer between the interfering particle and the measuring apparatus. It [...]texto impreso
We 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 fluctuat[...]texto impreso
We examine two simple and feasible practical schemes allowing the complete determination of any quantum measuring arrangement. This is illustrated with the example of parity measurement.texto impreso
We show that variance and Shannon entropy provide contradictory conclusions for the uncertainty associated with the number operator for some families of states of harmonic oscillator systems with fixed mean number, and for the uncertainty of a s[...]texto impreso
We assess the degree of coherence of vectorial electromagnetic fields in the space-frequency domain as the distance between the cross-spectral density matrix and the identity matrix representing completely incoherent light. This definition is co[...]texto impreso
Quantum optics entails polarization properties that cannot be fully described by the classical Stokes parameters. In this work, we characterize the polarization of classical as well as quantum fields by means of a probability distribution on the[...]texto impreso
We address a quantitative determination of the degree of polarization of type-II unpolarized light via the computation of the distance between the polarization distribution and the uniform distribution associated with fully unpolarized light (i.[...]texto impreso
We present an intuitive model of detector self-tomography. Two identical realizations of the detector are illuminated by an entangled state that connects the joint statistics in a way in which each detector sees the other as a kind of mirror ref[...]texto impreso
We find the observables that-can be determined by two practical schemes based on atom-field resonant interaction. In the first example, the interaction is followed by photon-number and atomic-population measurements. In the second scheme the dir[...]texto impreso
A full quantum analysis of 100% efficient interaction-free measurements is presented. It is shown that it is possible to describe consistently the phenomenon in terms of an effective interaction between object and apparatus that disturbs measura[...]texto impreso
We examine the evolution of a two-level atom when its population is monitored. The detection proposed is an interaction-fret measurement, so that the observation occurs without photon exchange between the atom and the apparatus. It is shown that[...]texto impreso
We show within a very simple framework that different measures of fluctuations lead to uncertainty relations resulting in contradictory conclusions. More specifically we focus on Tsallis and Renyi entropic uncertainty relations and we get that t[...]texto impreso
Ensemble approach to coherence between two scalar harmonic light vibrations and the phase difference
We develop an approach to coherence between two scalar harmonic light vibrations derived from the ensemble interpretation of statistical optics. Coherence is presented as a statistical variable itself that turns out to be the phase difference be[...]texto impreso
We compute Renyi entropies for the statistics of a noisy simultaneous observation of two complementary observables in two-dimensional quantum systems. The relative amount of uncertainty between two states depends on the uncertainty measure used.[...]texto impreso
We demonstrate that the superpositions of macroscopically distinct coherent states are maximally entangled states. Among other possible applications of this result, in this paper we show that the experimental arrangements generating superpositio[...]texto impreso
Martínez Matos, Óscar ; Alieva Krasheninnikova, Tatiana ; Canabal Boutureira, Héctor ; Navarrete Fernández, María de la Cruz ; Gonzalo Fonrodona, Isabel ; Herrera Fernández, José María ; Irigoyen Irigoyen, Maite ; Luis Aina, Alfredo ; Piquero Sanz, Gemma ; Rodrigo Martín Romo, José Augusto ; Sánchez Brea, Luis Miguel ; Sánchez Martín, José Antonio ; Serna Galán, Julio ; Tercero Gómez, José Luis ; Torcal Milla, Francisco José ; Vilas Prieto, José Luis ; Weigand Talavera, Rosa | 2015Se propone un cambio en la metodología docente de la asignatura Laboratorio de Física III del Grado en Física, para hacerla más dinámica y potenciar la participación e iniciativas de los estudiantes, adecuándola al espíritu de Boloniatexto impreso
We show that metrological resolution in the detection of small phase shifts provides a suitable generalization of the degrees of coherence and polarization. Resolution is estimated via Fisher information. Besides the standard two-beam Gaussian c[...]texto impreso
We propose a simple method to generate in practice the most general two-mode states with maximum entanglement. The method is based on energy-conserving dispersive interactions that can be easily implemented in different context such as quantum o[...]texto impreso
We analyze the quantum limit to the sensitivity of the detection of small displacements. We focus on the case of free particles and harmonic oscillators as the systems experiencing the displacement. We show that the minimum displacement detectab[...]texto impreso
We show that a single experiment can test simultaneously and independently both the nonclassicality of states and of measurements by the violation or fulfillment of classical bounds on the statistics. Nonideal measurements affected by imperfecti[...]texto impreso
We elaborate on a Hilbert-Schmidt distance measure assessing the intrinsic metrological accuracy in the detection of signals imprinted on quantum probe states by signal-dependent transformations. For small signals this leads to a probe-transform[...]texto impreso
We estimate the quantum state of a system between two measurements via a maximum likelihood strategy. This incorporates all the information provided by preselection and postselection in a legitimate quantum state. Moreover, it allows to include [...]texto impreso
We study the performance of linear and nonlinear optical schemes for the detection of weak signals for two classes of probe states. These are quadrature coherent squeezed states and the minimum uncertainty states of the generator of the transfor[...]texto impreso
A multimode quantum analysis of noise reduction in interferometric measurements is presented. A unitary transformation relating the output modes with the input ones for a Michelson interferometer with moving mirrors is given. The evaluation of t[...]texto impreso
Derivation and experimental violation of Bell-like inequalities involve the measurement of incompatible observables. Simple complementarity forbids the existence of such joint probability distribution. Moreover, the measurement of incompatible o[...]texto impreso
Nonclassicality cannot be a single-observable property, since the statistics of any quantum observable is compatible with classical physics. We develop a general procedure to reveal nonclassical behavior of light states from the joint statistics[...]texto impreso
Quantum polarization is investigated by means of a trajectory picture based on the Bohmian formulation of quantum mechanics. Relevant examples of classical-like two-mode field states are thus examined, namely, Glauber and SU(2) coherent states. [...]texto impreso
We study nonclassical polarization states characterized by polarization distributions taking negative values. We consider two different families of polarization distributions that include polarization analogs of the Wigner function. We apply dif[...]texto impreso
We 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 bound[...]texto impreso
We show that there are nonclassical states with lesser joint fluctuations of phase and number than any classical state. This is rather paradoxical since one would expect classical coherent states to be always of minimum uncertainty. The same res[...]texto impreso
We study nonclassicality in the product of the probabilities of noncommuting observables. We show that within the quantum theory, nonclassical states can provide larger probability product than classical states, so that nonclassical states appro[...]texto impreso
We 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 [...]texto impreso
We derive exceedingly simple practical procedures revealing the quantum nature of states and measurements by the violation of classical upper bounds on the statistics of arbitrary measurements. Data analysis is minimum, and definite conclusions [...]texto impreso
We derive simple practical tests revealing the quantum nature of states by the violation of classical upper bounds on the statistics of multiple outcomes of an observable. These criteria can be expressed in terms of the Kullback-Leibler divergen[...]texto impreso
We examine the performance of a nonlinear fiber gyroscope for improved signal detection beating the quantum limits of its linear counterparts. The performance is examined when the nonlinear gyroscope is illuminated by practical field states, suc[...]texto impreso
We 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 imperfection[...]texto impreso
Bermúdez, A. ; Martín Delgado, Miguel Ángel ; Luis Aina, Alfredo | American Physical Society | 2008-03-18We study the nonrelativistic limit of a paradigmatic model in relativistic quantum mechanics, the two-dimensional Dirac oscillator. Remarkably, we find a different kind of Zitterbewegung which persists in this nonrelativistic regime, and leads t[...]texto impreso
Fadel, Matteo ; Ares Santos, Laura ; Luis Aina, Alfredo ; He, Qiongyi | American Physical Society | 2020-05-22We use the uncertainty relation between the operators associated with the total number of particles and with the relative phase of two bosonic modes to construct entanglement and Einstein-Podolsky-Rosen steering criteria. These can be tested exp[...]texto impreso
We examine a case study where classical evolution emerges when observing a quantum evolution. By using a single-mode quantum Kerr evolution interrupted by measurement of the double-homodyne kind (projecting the evolved field state into classical[...]texto impreso
We present a fully operational and consistent approach to complementarity. In contrast to previous approaches, in this proposal the duality relations emerge exclusively from the outcomes of simultaneous measurements performed on every run of the[...]texto impreso
The problem of a correct quantum description of the phase difference is examined from the perspective of parameter estimation theory. It is shown that an optimum phase-shift measurement defines a phase difference operator which coincides with ot[...]texto impreso
We address a systematic approach to the study of the optimum states reaching maximum resolution for interferometers with moving mirrors. We find a correspondence between the optimum states for interferometers with fixed and moving mirrors.texto impreso
We introduce a unitary operator representing the exponential of the phase difference between two modes of the electromagnetic field. The eigenvalue spectrum has a discrete character that is fully analyzed. We relate this operator with a suitable[...]texto impreso
The quantum theory of light propagation in a Kerr medium is applied to describe changes in the polarization state of light. A number of purely quantum effects arising during the propagation are analyzed. Stokes operators and Pegg-Barnett formali[...]texto impreso
We propose a practical arrangement that allows one to reach the Heisenberg limit in precision phase-shift measurements. This is achieved via phase-shift amplification. The arrangement we propose is based on experimental processes already carried[...]texto impreso
We analyze the relation between the classical part of quantum observables and the distributions representing quantum states and observables on the classical phase space. We determine in which conditions such a relation can be established, and th[...]texto impreso
We introduce a probability distribution for polarization of three-dimensional quantum light fields as a marginal of the quadrature Q function for a three-mode field by removing the variables irrelevant for polarization (total intensity and globa[...]texto impreso
We propose a formal resource-theoretic approach to quantify the degree of polarization of two- and three-dimensional random electromagnetic fields. This endows the space of spectral polarization matrices with the orders induced by majorization o[...]texto impreso
We elucidate a ray picture of coherence for vectorial electromagnetic waves by using the Stokes parameters for light rays defined by the optical Wigner function. Paraxial propagation is formulated as a complementary Huygens principle. We show th[...]texto impreso
We formulate polarization uncertainty relations and polarization squeezing criteria in a SU(2) invariant manner. In this formulation the SU(2) coherent states are the only minimum uncertainty states. We show that polarization squeezing is a nonc[...]texto impreso
We examine whether the Stokes parameters of a two-mode electromagnetic field results from the superposition of the spins of the photons it contains. To this end we express any n-photon state as the result of the action on the vacuum of n creatio[...]texto impreso
Porras, Miguel A. ; Gonzalo Fonrodona, Isabel ; Luis Aina, Alfredo | American Physical Society | 2016-04-07We show that quantum Zeno dynamics can be mimicked by the isolated evolution of an unobserved system in an effective potential. Monitoring frequently whether a particle remains in a region of space leads to the same wave-packet dynamics as placi[...]texto impreso
We develop practical schemes for the measurement of the covariance matrix for intrinsic angular-momentum variables in quantum optics. We particularize this approach to two-beam polarimetry and interferometry, as well as to ensembles of two-level[...]texto impreso
We examine whether metrological resolution beyond coherent states is a nonclassical effect. We show that this is true for linear detection schemes but false for nonlinear schemes, and propose a very simple experimental setup to test it. We find [...]texto impreso
In this work we analyze the quantum phase properties of pairs of electromagnetic field modes. Since phases differing by 2? are physically indistinguishable, we propose a general procedure to obtain the correct mod(2?) probability distributions f[...]texto impreso
We investigate duality relations between conjugate observables after measurements performed on a single realization of the system. The application of standard inference methods implies the existence of duality relations for single systems when u[...]texto impreso
We develop a thorough connection between visibility, coherence, and phase statistics for N-dimensional quantum systems and N classical waves.texto impreso
We show the formal equivalence between the phase-space representations of transformations and quantum states. We study invariant quantum input-output transformations in phase space and in Hilbert space. We show that all invariant processes are l[...]texto impreso
We examine the relationship between nonseparable transformations and nonlinear optical processes, surpassing the Heisenberg limit in precision measurements.texto impreso
We introduce quantum states associated with single phase space points in the Wigner formalism for finite-dimensional spaces. We consider both continuous and discrete Wigner functions. This analysis provides a procedure for a direct practical obs[...]texto impreso
We derive quantum polarization distributions on the Poincare sphere for two-mode fields as suitable marginals of the standard s-ordered quadrature distributions that include the Wigner function. We compare them with previously introduced distrib[...]texto impreso
We study the polarization properties of three-dimensional quantum light fields by using the Stokes operators. We modify the standard definition of degree of polarization in order to encompass polarization properties in the quantum domain. We sho[...]texto impreso
The use of Rényi entropy as an uncertainty measure alternative to variance leads to the study of states with quantum fluctuations below the levels established by Gaussian states, which are the position-momentum minimum uncertainty states accordi[...]texto impreso
We present different schemes for preparing and maintaining the quantum state of multilevel systems. This is achieved via a suitable combination of coherent trapping and the Zeno effect which serves to protect the prepared state against undesired[...]texto impreso
We demonstrate the possibility of practical tomographic determination of arbitrary input-output transformations. It is shown that the Liouville-space formalism provides a generalization of standard tomography encompassing the reconstruction of p[...]texto impreso
Porras, Miguel A. ; Luis Aina, Alfredo ; Gonzalo Fonrodona, Isabel | American Physical Society | 2014Although the quantum Zeno effect takes its name from Zeno’s arrow paradox, the effect of frequently observing the position of a freely moving particle on its motion has not been analyzed in detail in the frame of standard quantum mechanics. We s[...]texto impreso
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 [...]texto impreso
Several quantum descriptions of the relative phase between an atomic dipole and a one-mode electromagnetic field are examined. Positive-operator measures for this variable are derived from dipole and field-phase formalisms. They are analyzed and[...]texto impreso
In 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 ?12 operator. In fact, we argue that it is a property common[...]texto impreso
We propose a formal resource-theoretic approach to assess the coherence between partially polarized electromagnetic fields. From this framework, we identify two resource theories for the vectorial coherence: polarization-sensitive coherence and [...]texto impreso
We show that there are extremely simple signal detection schemes where the finiteness of energy resources places no limit on the resolution. On the contrary, larger resolution can be obtained with lower energy. To this end the generator of the s[...]texto impreso
We address the propagation of the spin along classical trajectories for a spin-1/2 particle obeying the Dirac equation with scalar potentials. Focusing on classical trajectories as the exact propagation of wave-function discontinuities, we find [...]texto impreso
The states generated from the vacuum in two parametric down-conversion crystals with aligned idler beams are studied. It is shown that after a measurement of the photon number in some of the modes, the emerging states can be related to SU(2) and[...]texto impreso
We 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 exam[...]texto impreso
We provide evidence that the uncertainty in detection of small and deterministic phase-shift deviations from a working point can be lower than the Heisenberg bound, for a fixed finite mean number of photons. We achieve that by exploiting nonline[...]texto impreso
Weak-measurement-based experiments (Kocsis et al., 2011) have shown that, at least for pure states, the average evolution of independent photons in Young's two-slit experiment is in compliance with the trajectories prescribed by the Bohmian form[...]texto impreso
We present a simple multimode analysis of the Zeno and anti-Zeno effects in spontaneous parametric down-conversion. In this process the input vacuum is an unstable state decaying into a reservoir of down-converted modes by emitting a pair of pho[...]texto impreso
We examine the appearance of Zeno and anti-Zeno effects when the unitary evolution of a two-level system is observed. We demonstrate that, contrary to previous claims, the anti-Zeno effect can occur in two-level systems so that the observation c[...]texto impreso
Porras, Miguel A. ; Luis Aina, Alfredo ; Gonzalo Fonrodona, Isabel ; Sanz, Ángel S. | American Physical Society | 2011-11-14We analyze a simple and feasible practical scheme displaying Zeno, anti-Zeno, and inverse-Zeno effects in the observation of wave-packet spreading caused by free evolution. The scheme is valid both in spatial diffraction of classical optical wav[...]texto impreso
Luis Aina, Alfredo ; Gonzalo Fonrodona, Isabel ; Porras, Miguel A. | American Physical Society | 2013-06-20We describe a version of the Zeno effect where the monitored physical property cannot be represented by a standard operator in the system space and the evolution to be prevented by observation is not unitary. This is the case of quantum-state pu[...]texto impreso
Two examples are presented where the photon emission on spontaneous parametric down-conversion is prevented when attempts are made to infer the moment of emission. This inhibition is analyzed in terms of the disturbance caused on the system by t[...]