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
6 results
Search Results
Now showing 1 - 6 of 6
Item Zeno effect in degree of polarization of a single photon or quantum-state purity of a spin-1/2 system(Physical review A, 2013) Luis Aina, Alfredo; Gonzalo Fonrodona, Isabel; Porras, Miguel A.We 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 purity of a spin-1/2 system, which is equivalent to the degree of polarization of a single photon. By a suitable embedding of the system (say, a single photon) in an enlarged space of a pair of photons, pure and fully mixed components lead to orthogonal subspaces, with lack of purity becoming equivalent to entanglement. By imposing desirable properties the representation of the system in the enlarged space is unique. We show that the Zeno effect is possible, and experimentally feasible, in the enlarged space. The peculiarity that photons in identical polarization states are involved in pairs to observe the dynamics of each photon allows us to refer it as the self-Zeno effect or Narcissus effect.Item Classical Zeno dynamics in the light emitted by an extended, partially coherent source(Physical review A, 2013) Porras, Miguel A.; Luis Aina, Alfredo; Gonzalo Fonrodona, IsabelWe 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 spreading of the light emitted by an extended source results in a nontrivial dynamics where spreading and all other transverse effects associated with light propagation as the increase of spatial coherence tends to be inhibited. This is fully equivalent to a quantum Zeno dynamics where monitoring whether a quantum free particle at rest remains in a spatial interval causes inhibition of the quantum-state evolution, including the degree of purity.Item Zeno dynamics in wave-packet diffraction spreading(Physical review A, 2011) Porras, Miguel A.; Luis Aina, Alfredo; Gonzalo Fonrodona, Isabel; Sanz, Ángel S.We 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 waves and in time diffraction of a quantum wave packet. In the optical realization, diffraction spreading is observed by placing slits between a light source and a light-power detector. We show that the occurrence of Zeno or anti-Zeno effects depends just on the frequency of observations between the source and detector. These effects are seen to be related to the diffraction mode theory in Fabry-Perot resonators.Item Zeno inhibition of polarization rotation in an optically active medium(European journal of physics, 2015) Gonzalo Fonrodona, Isabel; Porras, Miguel A.; Luis Aina, AlfredoWe describe an experiment in which the rotation of the polarization of light propagating in an optically active water solution of D-fructose tends to be inhibited by frequent monitoring whether the polarization remains unchanged. This is an example of the Zeno effect that has remarkable pedagogical interest because of its conceptual simplicity, easy implementation, low cost, and because the same the Zeno effect holds at classical and quantum levels. An added value is the demonstration of the Zeno effect beyond typical idealized assumptions in a practical setting with real polarizers.Item Potential barrier mimicking frequent location measurements in quantum Zeno dynamics.(Physical review A, 2016) Porras, Miguel A.; Gonzalo Fonrodona, Isabel; Luis Aina, AlfredoWe 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 placing the region on top of a potential barrier and letting the particle evolve on its own, without external couplings. We focus on very frequent but not continuous observation so that the particle abandons the initial region with some finite probability. The height of the barrier relative to the surroundings for a high frequency. of the observations being mimicked is found numerically to be hν/2,where h is Planck's constant.Item Quantum Zeno effect for a free-moving particle(Physical review A, 2014) Porras, Miguel A.; Luis Aina, Alfredo; Gonzalo Fonrodona, IsabelAlthough 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 study the evolution of a moving free particle while monitoring whether it lingers in a given region of space, and explain the dependence of the lingering probability on the frequency of the measurements and the initial momentum of the particle. Stopping the particle entails the emergence of Schrödinger cat states during the observed evolution, closely connected to the high-order diffraction modes in Fabry-Pérot optical resonators.