Efficient photon counting and single-photon generation using resonant nonlinear optics

The behavior of an atomic double lambda system in the presence of a strong off-resonant classical field and a few-photon resonant quantum field is examined. It is shown that the system possesses properties that allow a single-photon state to be distilled from a multi-photon input wave packet. In addition, the system is also capable of functioning as an efficient photodetector discriminating between one- and two-photon wave packets with arbitrarily high efficiency.Comment: 4 pages, 2 figure

Evidence for an unconventional magnetic instability in the spin-tetrahedra system Cu_2Te_2O_5Br_2

Thermodynamic experiments as well as Raman scattering have been used to study the magnetic instabilities in the spin-tetrahedra systems Cu_2Te_2O_5X_2, X=Cl and Br. While the phase transition observed in the Cl system at T_o=18.2 K is consistent with 3D AF ordering, the phase transition at T_o=11.3 K in the Br system has several unusual features. We propose an explanation in terms of weakly coupled tetrahedra with a singlet-triplet gap and low lying singlets.Comment: 4 pages, 4 figure

Reinforcement of wood with natural fibers

This paper describes an experimental programme which examines the reinforcement in flexure of timber beams with composite materials based on natural fibers in the form of fabrics made from hemp, flax, basalt and bamboo fibers. The industrial use of natural fibers has been continuously increasing since 1990s due to their advantages in terms of production costs, pollution emissions and energy consumption for production and disposal. The technique allows the reinforcement of the intrados of beams, avoiding the dismantling of the overlying part of the structure with significant savings in terms of costs and work time. The test program consists of three phases incorporating 45 beams. The bending tests on the wooden elements made it possible to measure the increase in capacity and stiffness resulting from the composite reinforcement. This was applied to beams, creating different arrangements and using different quantities (number of layers). Despite the diversity of the various tests carried out, the results obtained in some cases showed significant increases in terms of load-carrying capacity and in deflection ductility

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

80hk Momentum Separation with Bloch Oscillations in an Optically Guided Atom Interferometer

We demonstrate phase sensitivity in a horizontally guided, acceleration-sensitive atom interferometer with a momentum separation of 80hk between its arms. A fringe visibility of 7% is observed. Our coherent pulse sequence accelerates the cold cloud in an optical waveguide, an inherently scalable route to large momentum separation and high sensitivity. We maintain coherence at high momentum separation due to both the transverse confinement provided by the guide, and our use of optical delta-kick cooling on our cold-atom cloud. We also construct a horizontal interferometric gradiometer to measure the longitudinal curvature of our optical waveguide.Comment: 6 pages, 6 figure

Optically guided linear Mach Zehnder atom interferometer

We demonstrate a horizontal, linearly guided Mach Zehnder atom interferometer in an optical waveguide. Intended as a proof-of-principle experiment, the interferometer utilises a Bose-Einstein condensate in the magnetically insensitive |F=1,mF=0> state of Rubidium-87 as an acceleration sensitive test mass. We achieve a modest sensitivity to acceleration of da = 7x10^-4 m/s^2. Our fringe visibility is as high as 38% in this optically guided atom interferometer. We observe a time-of-flight in the waveguide of over half a second, demonstrating the utility of our optical guide for future sensors.Comment: 6 pages, 3 figures. Submitted to Phys. Rev.

Full quantum solutions to the resonant four-wave mixing of two single-photon wave packets

We analyze both analytically and numerically the resonant four-wave mixing of two co-propagating single-photon wave packets. We present analytic expressions for the two-photon wave function and show that soliton-type quantum solutions exist which display a shape-preserving oscillatory exchange of excitations between the modes. Potential applications including quantum information processing are discussed.Comment: 7 pages, 3 figure

Reconstruction of 2D Al Ti on TiB in an aluminium melt

It has been widely considered that Al Ti is involved in the aluminium nucleation on TiB , although the mechanism has not been fully understood. In this paper molecular dynamics has been conducted to investigate this phenomenon at an atomistic scale. It was found that a two-dimensional Al Ti layer may remain on TiB above the aluminium liquidus. In addition, the results showed that this 2D Al Ti undergoes interface reconstruction by forming a triangular pattern. This triangular pattern consists of different alternative stacking sequences. The transition region between the triangles forms an area of strain concentration. By means of this mechanism, this interfacial Al Ti layer stabilizes itself by localizing the large misfit strain between TiB and Al Ti This reconstruction is similar to the hdp-fcc interface reconstruction in other systems which has been observed experimentally.EPSR

Earth-like aqueous debris-flow activity on Mars at high orbital obliquity in the last million years

Liquid water is currently extremely rare on Mars, but was more abundant during periods of high obliquity in the last few millions of years. This is testified by the widespread occurrence of mid-latitude gullies: small catchment-fan systems. However, there are no direct estimates of the amount and frequency of liquid water generation during these periods. Here we determine debris-flow size, frequency and associated water volumes in Istok crater, and show that debris flows occurred at Earth-like frequencies during high-obliquity periods in the last million years on Mars. Results further imply that local accumulations of snow/ice within gullies were much more voluminous than currently predicted; melting must have yielded centimetres of liquid water in catchments; and recent aqueous activity in some mid-latitude craters was much more frequent than previously anticipated

Attosecond pulse trains generated using two color laser fields

We investigate the spectral and temporal structure of high harmonic emission from argon exposed to an infrared laser field and its second harmonic. For a wide range of generating conditions, trains of attosecond pulses with only one pulse per infrared cycle are generated. The synchronization necessary for producing such trains ensures that they have a stable pulse-to-pulse carrier envelope phase, unlike trains generated from one color fields, which have two pulses per cycle and a π phase shift between consecutive pulses. Our experiment extends the generation of phase stabilized few cycle pulses to the extreme ultraviolet regime. © 2006 The American Physical Society