1,424 research outputs found
Antiferromagnetism in NiO Observed by Transmission Electron Diffraction
Neutron diffraction has been used to investigate antiferromagnetism since
1949. Here we show that antiferromagnetic reflections can also be seen in
transmission electron diffraction patterns from NiO. The diffraction patterns
taken here came from regions as small as 10.5 nm and such patterns could be
used to form an image of the antiferromagnetic structure with a nanometre
resolution.Comment: 10 pages, 7 figures. Typos corrected. To appear in Physical Review
Letter
Intensity fluctuations in steady state superradiance
Alkaline-earth like atoms with ultra-narrow optical transitions enable
superradiance in steady state. The emitted light promises to have an
unprecedented stability with a linewidth as narrow as a few millihertz. In
order to evaluate the potential usefulness of this light source as an
ultrastable oscillator in clock and precision metrology applications it is
crucial to understand the noise properties of this device. In this paper we
present a detailed analysis of the intensity fluctuations by means of
Monte-Carlo simulations and semi-classical approximations. We find that the
light exhibits bunching below threshold, is to a good approximation coherent in
the superradiant regime, and is chaotic above the second threshold.Comment: 8 pages, 5 figure
Extension of the Huttner-Barnett model to a magnetodielectric medium
The HuttnerBarnett model is extended to a magnetodielectric medium by
adding a new matter field to this model. The eigenoperators for the coupled
system are calculated and electromagnetic field is written in terms of these
operators. The electric and magnetic susceptibility of the medium are
explicitly derived and shown to satisfy the KramersKronig relations. It is
shown that the results obtained in this model are equivalent to the results
obtained from the phenomenological methods.Comment: 25 page
Interference of composite bosons
We investigate multi-boson interference. A Hamiltonian is presented that
treats pairs of bosons as a single composite boson. This Hamiltonian allows two
pairs of bosons to interact as if they were two single composite bosons. We
show that this leads to the composite bosons exhibiting novel interference
effects such as Hong-Ou-Mandel interference. We then investigate
generalizations of the formalism to the case of interference between two
general composite bosons. Finally, we show how one can realize interference
between composite bosons in the two atom Dicke model
Very weak electron-phonon coupling and strong strain coupling in manganites
The coupling of the manganite stripe phase to the lattice and to strain has
been investigated via transmission electron microscopy studies of
polycrystalline and thin film manganites. In polycrystalline \PCMOfiftwo a
lockin to in a sample with has been observed for the first
time. Such a lockin has been predicted as a key part of the Landau CDW theory
of the stripe phase. Thus it is possible to constrain the size of the
electron-phonon coupling in the CDW Landau theory to between 0.04% and 0.05% of
the electron-electron coupling term. In the thin film samples, films of the
same thickness grown on two different substrates exhibited different
wavevectors. The different strains present in the films on the two substrates
can be related to the wavevector observed via Landau theory. It is demonstrated
that the the elastic term which favours an incommensurate modulation has a
similar size to the coupling between the strain and the wavevector, meaning
that the coupling of strain to the superlattice is unexpectedly strong.Comment: 6 pages, 7 figure
All-Optical Switching Using the Quantum Zeno Effect and Two-Photon Absorption
We have previously shown that the quantum Zeno effect can be used to
implement quantum logic gates for quantum computing applications, where the
Zeno effect was produced using a strong two-photon absorbing medium. Here we
show that the Zeno effect can also be used to implement classical logic gates
whose inputs and outputs are high-intensity fields (coherent states). The
operation of the devices can be understood using a quasi-static analysis, and
their switching times are calculated using a dynamic approach. The two-photon
absorption coefficient of rubidium vapor is shown to allow operation of these
devices at relatively low power levels.Comment: 21 pages, 11 figures. Submitted to Phys. Rev.
Daylighting: appraisal at the early design stages
For a building design team concerned with the quality of the internal environment of buildings the percentage area of glazing on a building facade is one of the most useful criteria for judging the building envelope as a modifier of climate at early design stages since it is at the window that the various environmental parameters (heat, light and sound) remain only minimally modified.
The percentage area of glazing can be used to relate the numerous and often conflicting functions of the window such as the provision of daylight, summer time teperatures, sound insulation, energy efficiency and view satisfaction
A molecular theory for two-photon and three-photon fluorescence polarization
In the analysis of molecular structure and local order in heterogeneous samples, multiphoton excitation of fluorescence affords chemically specific information and high-resolution imaging. This report presents the results of an investigation that secures a detailed theoretical representation of the fluorescence polarization produced by one-, two-, and three-photon excitations, with orientational averaging procedures being deployed to deliver the fully disordered limits. The equations determining multiphoton fluorescence response prove to be expressible in a relatively simple, generic form, and graphs exhibit the functional form of the multiphoton fluorescence polarization. Amongst other features, the results lead to the identification of a condition under which the fluorescence produced through the concerted absorption of any number of photons becomes completely unpolarized. It is also shown that the angular variation of fluorescence intensities is reliable indicator of orientational disorder
Polarization entanglement visibility of photon pairs emitted by a quantum dot embedded in a microcavity
We study the photon emission from a quantum dot embedded in a microcavity.
Incoherent pumping of its excitons and biexciton provokes the emission of leaky
and cavity modes. By solving a master equation we obtain the correlation
functions required to compute the spectrum and the relative efficiency among
the emission of pairs and single photons. A quantum regime appears for low
pumping and large rate of emission. By means of a post-selection process, a two
beams experiment with different linear polarizations could be performed
producing a large polarization entanglement visibility precisely in the quantum
regime.Comment: 13 pages and 6 figure
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