1,926 research outputs found
Bi-photon propagation control with optimized wavefront by means of Adaptive Optics
We present an efficient method to control the spatial modes of entangled
photons produced through SPDC process. Bi-photon beam propagation is controlled
by a deformable mirror, that shapes a 404nm CW diode laser pump interacting
with a nonlinear BBO type-I crystal. Thanks to adaptive optical system, the
propagation of 808nm SPDC light produced is optimized over a distance of 2m.
The whole system optimization is carried out by a feedback between deformable
mirror action and entangled photon coincidence counts. We also demonstrated the
improvement of the two-photon coupling into single mode fibers
Nondestructive measurement of intensity of optical fields using spontaneous parametric down conversion
Results of nondestructive measurements of intensity (photons per mode) of light from different sources are discussed. The procedure of measurement does not destroy the state of the optical field. The method is based on using the second order nonlinearity of crystal media lacking a center of symmetry and the nonclassical properties of the process of Spontaneous Parametric Down Conversion (SPDC)
Role of the Dzyaloshinskii-Moriya interaction in multiferroic perovskites
With the perovskite multiferroic RMnO3 (R = Gd, Tb, Dy) as guidance, we argue
that the Dzyaloshinskii-Moriya interaction (DMI) provides the microscopic
mechanism for the coexistence and strong coupling between ferroelectricity and
incommensurate magnetism. We use Monte-Carlo simulations and zero temperature
exact calculations to study a model incorporating the double-exchange,
superexchange, Jahn-Teller and DMI terms. The phase diagram contains a
multiferroic phase between A and E antiferromagnetic phases, in excellent
agreement with experiments.Comment: 6 pages, 5 figure
Twin-photon techniques for photo-detector calibration
The aim of this review paper is to enlighten some recent progresses in
quantum optical metrology in the part of quantum efficiency measurements of
photo-detectors performed with bi-photon states. The intrinsic correlated
nature of entangled photons from Spontaneous Parametric Down Conversion
phenomenon has opened wide horizons to a new approach for the absolute
measurement of photo-detector quantum efficiency, outgoing the requirement for
conventional standards of optical radiation; in particular the simultaneous
feature of the creation of conjugated photons led to a well known technique of
coincidence measurement, deeply understood and implemented for standard uses.
On the other hand, based on manipulation of entanglement developed for Quantum
Information protocols implementations, a new method has been proposed for
quantum efficiency measurement, exploiting polarisation entanglement in
addition to energy-momentum and time ones, that is based on conditioned
polarisation state manipulation. In this review, after a general discussion on
absolute photo-detector calibration, we compare these different methods, in
order to give an accurate operational sketch of the absolute quantum efficiency
measurement state of the art
Absolute calibration of Analog Detectors using Stimulated Parametric Down Conversion
Spontaneous parametric down conversion has been largely exploited as a tool
for absolute calibration of photon counting detectors, photomultiplier tubes or
avalanche photodiodes working in Geiger regime. In this work we investigate the
extension of this technique from very low photon flux of photon counting regime
to the absolute calibration of analog photodetectors at higher photon flux.
Moving toward higher photon rate, i.e. at high gain regime, with the
spontaneous parametric down conversion shows intrinsic limitations of the
method, while the stimulated parametric down conversion process, where a seed
beam properly injected into the crystal in order to increase the photon
generation rate in the conjugate arm, allows us to work around this problem. A
preliminary uncertainty budget is discussed
Order parameter in superconductors with non-degenerate bands
In noncentrosymmetric metals, the spin degeneracy of the electronic bands is
lifted by spin-orbit coupling. We consider general symmetry properties of the
pairing function Delta(k) in noncentrosymmetric superconductors with spin-orbit
coupling (NSC), including CePt3Si, UIr and Cd2Re2O7. We find that Delta(k) =
chi(k) t(k), where chi(k) is an even function which transforms according to the
irreducible representations of the crystallographic point group and t(k) is a
model dependent phase factor. We consider tunnelling between a NSC and a
conventional superconductor. It is found that, in terms of thermodynamical
properties as well as the Josephson effect, the state of NSC resembles a
singlet superconducting state with gap function chi(k).Comment: 8 pages, references updated. Accepted to PR
On the effect of anomalous photoabsorption in parametric X radiation
The parametric X radiation of relativistic electrons passing through a monocrystal is considered. It is demonstrated that, contrary to widespread option, conditions for the effect of anomalous photoabsorption to show up can be realized in the Laue scattering geometryye
- …