807 research outputs found
Quantum noise in ideal operational amplifiers
We consider a model of quantum measurement built on an ideal operational
amplifier operating in the limit of infinite gain, infinite input impedance and
null output impedance and with a feddback loop. We evaluate the intensity and
voltage noises which have to be added to the classical amplification equations
in order to fulfill the requirements of quantum mechanics. We give a
description of this measurement device as a quantum network scattering quantum
fluctuations from input to output ports.Comment: 4 pages, 2 figures, RevTe
Conditional preparation of a quantum state in the continuous variable regime: generation of a sub-Poissonian state from twin beams
We report the first experimental demonstration of conditional preparation of
a non classical state of light in the continuous variable regime. Starting from
a non degenerate OPO which generates above threshold quantum intensity
correlated signal and idler "twin beams", we keep the recorded values of the
signal intensity only when the idler falls inside a band of values narrower
than its standard deviation. By this very simple technique, we generate a
sub-Poissonian state 4.4dB below shot noise from twin beams exhibiting 7.5dB of
noise reduction in the intensity difference.Comment: 4 pages, Accepted in Phys. Rev. Let
Casimir torque between corrugated metallic plates
We consider two parallel corrugated plates and show that a Casimir torque
arises when the corrugation directions are not aligned. We follow the
scattering approach and calculate the Casimir energy up to second order in the
corrugation amplitudes, taking into account nonspecular reflections,
polarization mixing and the finite conductivity of the metals. We compare our
results with the proximity force approximation, which overestimates the torque
by a factor 2 when taking the conditions that optimize the effect. We argue
that the Casimir torque could be measured for separation distances as large as
1 Comment: 7 pages, 3 figures, contribution to QFEXT07 proceeding
Vacuum induced torque between corrugated metallic plates
We study the torque arising between two corrugated metallic plates due to the
interaction with electromagnetic vacuum. This Casimir torque can be measured
with torsion pendulum techniques for separation distances as large as 1m.
It allows one to probe the nontrivial geometry dependence of the Casimir energy
in a configuration which can be evaluated theoretically with accuracy. In the
optimal experimental configuration, the commonly used proximity force
approximation turns out to overestimate the torque by a factor 2 or larger.Comment: 7 pages, 4 figures, to appear in Europhysics Letters. Technical
problem with eps file for figure 4 was fixe
Quantum fluctuations for drag free geodesic motion
The drag free technique is used to force a proof mass to follow a geodesic
motion. The mass is protected from perturbations by a cage, and the motion of
the latter is actively controlled to follow the motion of the proof mass. We
present a theoretical analysis of the effects of quantum fluctuations for this
technique. We show that a perfect drag free operation is in principle possible
at the quantum level, in spite of the back action exerted on the mass by the
position sensor.Comment: 4 pages, 1 figure, RevTeX, minor change
Flying phase mask for the printing of long submicron-period stitchingless gratings
International audienceLong and stitchingless gratings are printed by means of a read/write head comprising a phase mask illuminated by an intensity modulated laser beam and a reference grating displacement sensor which dictates the modulation period real time. A nearly perfect grating copying is achieved by fixing the sensor grating scale and the written grating substrate on a long platform sliding under the read/write hea
Structural insights into Clostridium perfringens delta toxin pore formation
Clostridium perfringens Delta toxin is one of the three hemolysin-like proteins produced by C. perfringens type C and possibly type B strains. One of the others, NetB, has been shown to be the major cause of Avian Nectrotic Enteritis, which following the reduction in use of antibiotics as growth promoters, has become an emerging disease of industrial poultry. Delta toxin itself is cytotoxic to the wide range of human and animal macrophages and platelets that present GM2 ganglioside on their membranes. It has sequence similarity with Staphylococcus aureus β-pore forming toxins and is expected to heptamerize and form pores in the lipid bilayer of host cell membranes. Nevertheless, its exact mode of action remains undetermined. Here we report the 2.4 Å crystal structure of monomeric Delta toxin. The superposition of this structure with the structure of the phospholipid-bound F component of S. aureus leucocidin (LukF) revealed that the glycerol molecules bound to Delta toxin and the phospholipids in LukF are accommodated in the same hydrophobic clefts, corresponding to where the toxin is expected to latch onto the membrane, though the binding sites show significant differences. From structure-based sequence alignment with the known structure of staphylococcal α-hemolysin, a model of the Delta toxin pore form has been built. Using electron microscopy, we have validated our model and characterized the Delta toxin pore on liposomes. These results highlight both similarities and differences in the mechanism of Delta toxin (and by extension NetB) cytotoxicity from that of the staphylococcal pore-forming toxins
Plaquette Ordering in SU(4) Antiferromagnets
We use fermion mean field theory to study possible plaquette ordering in the
antiferromagnetic SU(4) Heisenberg model. We find the ground state for both the
square and triangular lattices to be the disconnected plaquette state. Our mean
field theory gives a first order transition for plaquette ordering for the
triangular lattice. Our results suggest a large number of low lying states.Comment: 16 pages, 5 figure
Optical security device for document protection using plasmon resonant transmission through a thin corrugated metallic film embedded in a plastic foil
The well known resonant or extraordinary transmission through an undulated metallic thin film embedded in a dielectric layer using the Plasmon modes excitation under normal incidence is industrially exploited for document protection applications. While the effect is very spectrally sensitive to the incidence angle in collinear incidence since it leads to a transmission peak separation in two peaks, it is very tolerant in conical incidence (incidence angle in the plan normal to the grating direction). This property is used to create color transmission effects by playing with the sample rotation in the two directions to enhance the contrast of such effect. Theoretical approach, modeling and experimental demonstration in the visible range on a flexible plastic foil are presented for a see-through window implemented in document security
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