80 research outputs found
Entanglement in bipartite generalized coherent states
Entanglement in a class of bipartite generalized coherent states is
discussed. It is shown that a positive parameter can be associated with the
bipartite generalized coherent states so that the states with equal value for
the parameter are of equal entanglement. It is shown that the maximum possible
entanglement of 1 bit is attained if the positive parameter equals .
The result that the entanglement is one bit when the relative phase between the
composing states is in bipartite coherent states is shown to be true for
the class of bipartite generalized coherent states considered.Comment: 10 pages, 4 figures; typos corrected and figures redrawn for better
clarit
Entanglement concentration of continuous variable quantum states
We propose two probabilistic entanglement concentration schemes for a single
copy of two-mode squeezed vacuum state. The first scheme is based on the
off-resonant interaction of a Rydberg atom with the cavity field while the
second setup involves the cross Kerr interaction, auxiliary mode prepared in a
strong coherent state and a homodyne detection. We show that the
continuous-variable entanglement concentration allows us to improve the
fidelity of teleportation of coherent states.Comment: 7 pages, 7 figure
Dendritic cell-specific deletion of β-catenin results in fewer regulatory T-cells without exacerbating autoimmune collagen-induced arthritis
Dendritic cells (DCs) are professional antigen presenting cells that have the dual ability to stimulate immunity and maintain tolerance. However, the signalling pathways mediating tolerogenic DC function in vivo remain largely unknown. The β-catenin pathway has been suggested to promote a regulatory DC phenotype. The aim of this study was to unravel the role of β-catenin signalling to control DC function in the autoimmune collagen-induced arthritis model (CIA). Deletion of β-catenin specifically in DCs was achieved by crossing conditional knockout mice with a CD11c-Cre transgen
The Biology Instrument for the Viking Mars Mission
Two Viking spacecraft have successfully soft landed on the surface of Mars. Each carries, along with other scientific instruments, one biology laboratory with three different experiments designed to search for evidence of living microorganisms in material sampled from the Martian surface. This 15.5-kg biology instrument which occupies a volume of almost 28.3 dm3 is the first to carry out an in situ search for extraterrestrial life on a planet. The three experiments are called the pyrolytic release, labeled release, and gas exchange. The pyrolytic release experiment has the capability to measure the fixation of carbon dioxide or carbon monoxide into organic matter. The labeled release experiment detects metabolic processes by monitoring the production of volatile carbon compounds from a radioactively labeled nutrient mixture. The gas exchange experiment monitors the gas changes in the head space above a soil sample which is either incubated in a humid environment or supplied with a rich organic nutrient solution. Each experiment can analyze a soil sample as it is received from the surface or, as a control, analyze a soil which has been heated to above 160C. Each instrument has the capability to receive four different soils dug from the Martian surface and perform a number of analysis cycles depending on the particular experiment. This paper describes in detail the design and operation of the three experiments and the supporting subsystems
Teleportation improvement by conditional measurements on the two-mode squeezed vacuum
We show that by making conditional measurements on the Einstein-Podolsky-Rosen (EPR) squeezed vacuum [T. Opatrny, G. Kurizki, and D.-G. Welsch, Phys. Rev. A 61, 032302 (2000)], one can improve the efficacy of teleportation for both the position-difference, momentum-sum, and number-difference, phase-sum continuous variable teleportation protocols. We investigate the relative abilities of the standard and conditional EPR states, and show that by conditioning we can improve the fidelity of teleportation of coherent states from below to above the (F) over bar =2/3 boundary, thereby achieving unambiguously quantum teleportation
Mesoscopic models for DNA stretching under force: new results and comparison to experiments
Single molecule experiments on B-DNA stretching have revealed one or two
structural transitions, when increasing the external force. They are
characterized by a sudden increase of DNA contour length and a decrease of the
bending rigidity. It has been proposed that the first transition, at forces of
60--80 pN, is a transition from B to S-DNA, viewed as a stretched duplex DNA,
while the second one, at stronger forces, is a strand peeling resulting in
single stranded DNAs (ssDNA), similar to thermal denaturation. But due to
experimental conditions these two transitions can overlap, for instance for
poly(dA-dT). We derive analytical formula using a coupled discrete worm like
chain-Ising model. Our model takes into account bending rigidity, discreteness
of the chain, linear and non-linear (for ssDNA) bond stretching. In the limit
of zero force, this model simplifies into a coupled model already developed by
us for studying thermal DNA melting, establishing a connexion with previous
fitting parameter values for denaturation profiles. We find that: (i) ssDNA is
fitted, using an analytical formula, over a nanoNewton range with only three
free parameters, the contour length, the bending modulus and the monomer size;
(ii) a surprisingly good fit on this force range is possible only by choosing a
monomer size of 0.2 nm, almost 4 times smaller than the ssDNA nucleobase
length; (iii) mesoscopic models are not able to fit B to ssDNA (or S to ss)
transitions; (iv) an analytical formula for fitting B to S transitions is
derived in the strong force approximation and for long DNAs, which is in
excellent agreement with exact transfer matrix calculations; (v) this formula
fits perfectly well poly(dG-dC) and -DNA force-extension curves with
consistent parameter values; (vi) a coherent picture, where S to ssDNA
transitions are much more sensitive to base-pair sequence than the B to S one,
emerges.Comment: 14 pages, 9 figure
Ultra-High-Speed Optical Serial-to-Parallel Data Conversion in a Silicon Nanowire
We demonstrate conversion from 64×10 Gbit/s OTDM to 25 GHz DWDM by time-domain optical Fourier transformation. Using a single silicon nanowire, 40 of 64 OTDM tributaries are simultaneously converted to DWDM channels within FEC limits.</p
Multiorder coherent Raman scattering of a quantum probe field
We study the multiorder coherent Raman scattering of a quantum probe field in
a far-off-resonance medium with a prepared coherence. Under the conditions of
negligible dispersion and limited bandwidth, we derive a Bessel-function
solution for the sideband field operators. We analytically and numerically
calculate various quantum statistical characteristics of the sideband fields.
We show that the multiorder coherent Raman process can replicate the
statistical properties of a single-mode quantum probe field into a broad comb
of generated Raman sidebands. We also study the mixing and modulation of photon
statistical properties in the case of two-mode input. We show that the prepared
Raman coherence and the medium length can be used as control parameters to
switch a sideband field from one type of photon statistics to another type, or
from a non-squeezed state to a squeezed state and vice versa.Comment: 12 pages, 7 figures, to be published in Phys. Rev.
Measurement-induced nonlinearity in linear optics
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