115 research outputs found
Health surveillance and geography: Theoretical and methodological potential
Objectives: To contribute to constructing recognition methodologies in the field by means of secondary data on objects and their forms, namely conditions of action and means of existence of human endeavor; to contribute to health surveillance through the incorporation of particular geographic characteristics; to relate concepts and categories of the territorialization process of health surveillance practices
Energy and momentum entanglement in parametric downconversion
We present a simple treatment for the phenomenon of parametric downconversion
considering the coherent scattering of one pump photon into a photon pair by a
nonlinear crystal. The energy and momentum entanglement of the quantum state of
the generated twin photons are seen as a consequence of the fundamental
indistinguishability of the time and the position in which the photon pair is
created inside the crystal. We also discuss some consequences of the system
entanglement.Comment: 6 pages, 2 figures. v3: Minor changes on the text. Some references
were include
Experimental observation of spatial antibunching of photons
We report an interference experiment that shows transverse spatial
antibunching of photons. Using collinear parametric down-conversion in a
Young-type fourth-order interference setup we show interference patterns that
violate the classical Schwarz inequality and should not exist at all in a
classical description.Comment: 4 pages, 7 figure
Cancellation of atmospheric turbulence effects in entangled two-photon beams
Turbulent airflow in the atmosphere and the resulting random fluctuations in
its refractive index have long been known as a major cause of image
deterioration in astronomical imaging and figures among the obstacles for
reliable optical communication when information is encoded in the spatial
profile of a laser beam. Here we show that using correlation imaging and a
suitably prepared source of photon pairs, the most severe of the disturbances
inflicted on the beam by turbulence can be cancelled out. Other than a
two-photon light source, only linear passive optical elements are needed and,
as opposed to adaptive optics techniques, our scheme does not rely on active
wavefront correction.Comment: 5 pages, 3 figure
Hong-Ou-Mandel interferometer with cavities: theory
We study the number of coincidences in a Hong-Ou-Mandel interferometer exit
whose arms have been supplemented with the addition of one or two optical
cavities. The fourth-order correlation function at the beam-splitter exit is
calculated. In the regime where the cavity length are larger than the
one-photon coherence length, photon coalescence and anti-coalescence
interference is observed. Feynman's path diagrams for the indistinguishable
processes that lead to quantum interference are presented. As application for
the Hong-Ou-Mandel interferometer with two cavities, it is discussed the
construction of an optical XOR gate
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