2,184 research outputs found
Cavity-free nondestructive detection of a single optical photon
Detecting a single photon without absorbing it is a long standing challenge
in quantum optics. All experiments demonstrating the nondestructive detection
of a photon make use of a high quality cavity. We present a cavity free scheme
for nondestructive single-photon detection. By pumping a nonlinear medium we
implement an inter-field Rabi-oscillation which leads to a ?pi phase shift on
weak probe coherent laser field in the presence of a single signal photon
without destroying the signal photon. Our cavity-free scheme operates with a
fast intrinsic time scale in comparison with similar cavity-based schemes. We
implement a full real-space multimode numerical analysis of the interacting
photonic modes and confirm the validity of our nondestructive scheme in the
multimode case.Comment: 4 figures, 5 page
Sustainable water services and interaction with water resources in Europe and in Brazil
International audienceThe increasing interaction between large cities and nature makes "urban water" an issue: water resources and water services - including public water supply, sewage collection and treatment, and in large cities, storm water control -, which had become separate issues thanks to the process of water transport and treatment technologies, are now increasingly interfering with each other. We cannot take nature for granted anymore, and we need to protect water resources, if only to reduce the long term cost of transporting and treating water. In this paper, we compare the historical development of water industry technologies in European and Brazilian metropolitan areas, in their socio-economic and political context, tracing it through three "ages" of water technology and services which developed under civil engineering, sanitary engineering, and environmental engineering perspectives: the "quantity of water" and civil engineering paradigm was developed on the assumption that water should be drawn from natural environments far from the cities; in the "water quality" and chemical/sanitation engineering paradigm, water treatment was invented and allowed cities to take water from rivers closer to them and treat it, but also to reduce sewer discharge impacts; finally, the environmental engineering paradigm proposes to overcome the supply side perspective, by introducing demand side management, water conservation, water allocation flexibilisation, and an integrated approach to water services, water resources management, and land use policies
Paired atom laser beams created via four-wave mixing
A method to create paired atom laser beams from a metastable helium atom
laser via four-wave mixing is demonstrated. Radio frequency outcoupling is used
to extract atoms from a Bose Einstein condensate near the center of the
condensate and initiate scattering between trapped and untrapped atoms. The
unequal strengths of the interactions for different internal states allows an
energy-momentum resonance which leads to the creation of pairs of atoms
scattered from the zero-velocity condensate. The resulting scattered beams are
well separated from the main atom laser in the 2-dimensional transverse atom
laser profile. Numerical simulations of the system are in good agreement with
the observed atom laser spatial profiles, and indicate that the scattered beams
are generated by a four-wave mixing process, suggesting that the beams are
correlated.Comment: 5 pages, 3 figure
A multibeam atom laser: coherent atom beam splitting from a single far detuned laser
We report the experimental realisation of a multibeam atom laser. A single
continuous atom laser is outcoupled from a Bose-Einstein condensate (BEC) via
an optical Raman transition. The atom laser is subsequently split into up to
five atomic beams with slightly different momenta, resulting in multiple,
nearly co-propagating, coherent beams which could be of use in interferometric
experiments. The splitting process itself is a novel realization of Bragg
diffraction, driven by each of the optical Raman laser beams independently.
This presents a significantly simpler implementation of an atomic beam
splitter, one of the main elements of coherent atom optics
Cnidaria, Scleractinia, Siderastreidae, Siderastrea siderea (Ellis and Solander, 1786): Hartt Expedition and the first record of a Caribbean siderastreid in tropical Southwestern Atlantic
Samples of Siderastrea collected by the geologist C. F. Hartt during expedition to Brazil (19th century), anddeposited at the National Museum of the Natural History, Smithsonian Institution, have been re-examined. Taxonomicalanalyses resulted in the identification of a colony of S. siderea from offshore northern Bahia state. Following recentstudies, the occurrence of Caribbean siderastreids to western South Atlantic provides new criteria to assess intra- andinterpopulational morphological variation of the endemic S. stellata, refuting historical trends of synonymizations possiblybiased by long-term taxonomical misunderstandings
Erratum : Squeezing and entanglement delay using slow light
An inconsistency was found in the equations used to calculate the variance of
the quadrature fluctuations of a field propagating through a medium
demonstrating electromagnetically induced transparency (EIT). The decoherence
term used in our original paper introduces inconsistency under weak probe
approximation. In this erratum we give the Bloch equations with the correct
dephasing terms. The conclusions of the original paper remain the same. Both
entanglement and squeezing can be delayed and preserved using EIT without
adding noise when the decoherence rate is small.Comment: 1 page, no figur
Generation of directional, coherent matter beams through dynamical instabilities in Bose-Einstein condensates
We present a theoretical analysis of a coupled, two-state Bose-Einstein
condensate with non-equal scattering lengths, and show that dynamical
instabilities can be excited. We demonstrate that these instabilities are
exponentially amplified resulting in highly-directional,
oppositely-propagating, coherent matter beams at specific momenta. To
accomplish this we prove that the mean field of our system is periodic, and
extend the standard Bogoliubov approach to consider a time-dependent, but
cyclic, background. This allows us to use Floquet's theorem to gain analytic
insight into such systems, rather than employing the usual Bogoliubov-de Gennes
approach, which is usually limited to numerical solutions. We apply our theory
to the metastable Helium atom laser experiment of Dall et al. [Phys. Rev. A 79,
011601(R) (2009)] and show it explains the anomalous beam profiles they
observed. Finally we demonstrate the paired particle beams will be
EPR-entangled on formation.Comment: Corrected reference
Two-photon double ionization of neon using an intense attosecond pulse train
We present the first demonstration of two-photon double ionization of neon
using an intense extreme ultraviolet (XUV) attosecond pulse train (APT) in a
photon energy regime where both direct and sequential mechanisms are allowed.
For an APT generated through high-order harmonic generation (HHG) in argon we
achieve a total pulse energy close to 1 J, a central energy of 35 eV and a
total bandwidth of eV. The APT is focused by broadband optics in a
neon gas target to an intensity of Wcm. By tuning
the photon energy across the threshold for the sequential process the double
ionization signal can be turned on and off, indicating that the two-photon
double ionization predominantly occurs through a sequential process. The
demonstrated performance opens up possibilities for future XUV-XUV pump-probe
experiments with attosecond temporal resolution in a photon energy range where
it is possible to unravel the dynamics behind direct vs. sequential double
ionization and the associated electron correlation effects
Can optical squeezing be generated via polarization self-rotation in a thermal vapour cell?
The traversal of an elliptically polarized optical field through a thermal
vapour cell can give rise to a rotation of its polarization axis. This process,
known as polarization self-rotation (PSR), has been suggested as a mechanism
for producing squeezed light at atomic transition wavelengths. In this paper,
we show results of the characterization of PSR in isotopically enhanced
Rubidium-87 cells, performed in two independent laboratories. We observed that,
contrary to earlier work, the presence of atomic noise in the thermal vapour
overwhelms the observation of squeezing. We present a theory that contains
atomic noise terms and show that a null result in squeezing is consistent with
this theory.Comment: 10 pages, 11 figures, submitted to PRA. Please email author for a PDF
file if the article does not appear properl
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