4,142 research outputs found
Quantum Noise in Multipixel Image Processing
We consider the general problem of the quantum noise in a multipixel
measurement of an optical image. We first give a precise criterium in order to
characterize intrinsic single mode and multimode light. Then, using a
transverse mode decomposition, for each type of possible linear combination of
the pixels' outputs we give the exact expression of the detection mode, i.e.
the mode carrying the noise. We give also the only way to reduce the noise in
one or several simultaneous measurements.Comment: 8 pages and 1 figur
Non-linear and quantum optics of a type II OPO containing a birefringent element Part 1: Classical operation
We describe theoretically the main characteristics of the steady state regime
of a type II Optical Parametric Oscillator (OPO) containing a birefringent
plate. In such a device the signal and idler waves are at the same time
linearly coupled by the plate and nonlinearly coupled by the
crystal. This mixed coupling allows, in some well-defined range of the control
parameters, a frequency degenerate operation as well as phase locking between
the signal and idler modes. We describe here a complete model taking into
account all possible effects in the system, \emph{i.e.} arbitrary rotation of
the waveplate, non perfect phase matching, ring and linear cavities. This model
is able to explain the detailed features of the experiments performed with this
system.Comment: To be published in EPJ
From spin-Peierls to superconductivity: (TMTTF)_2PF_6 under high pressure
The nature of the attractive electron-electron interaction, leading to the
formation of Cooper-pairs in unconventional superconductors has still to be
fully understood and is subject to intensive research. Here we show that the
sequence spin-Peierls, antiferromagnetism, superconductivity observed in
(TMTTF)_2PF_6 under pressure makes the (TM)_2X phase diagram universal. We
argue that the suppression of the spin-Peierls transition under pressure, the
close vicinity of antiferromagnetic and superconducting phases at high pressure
as well as the existence of critical antiferromagnetic fluctuations above T_c
strongly support the intriguing possibility that the interchain exchange of
antiferromagnetic fluctuations provides the pairing mechanism required for
bound charge carriers.Comment: 4 pages, revtex, 4 figures (jpeg,eps,png
Bubble and Slug Flow at Microgravity Conditions: State of Knowledge and Open Questions
Based on the experiments carried out over the past decade at microgravity conditions, an overview of our current knowledge of bubbly and slug flows is presented. The transition from bubble to slug flow, the void fraction and the pressure drop are discussed from the data collected in the literature. The transition from bubble to slug flow may be predicted by introducing a critical void fraction that depends on the fluid properties and the pipe diameter; however, the role of coalescence which controls this transition is not clearly understood. The void fraction may be accurately calculated using a drift-flux model. It is shown from local measurements that the drift of the gas with respect to the mixture is due to non-uniform radial distribution of void fraction. The pressure drop happens to be controlled by the liquid flow for bubbly flow whereas for slug flow the experimental results show that pressure drops is larger than expected. From this study, the guidelines for future research in microgravity are given
Non-linear and quantum optics of a type II OPO containing a birefringent element Part 2 : bright entangled beams generation
We describe theoretically the quantum properties of atype-II Optical
Parametric Oscillator containing a birefringent plate which induces a linear
coupling between the orthogonally polarized signal and idler beams and results
in phase locking between these two beams. As in a classical OPO, the signal and
idler waves show large quantum correlations which can be measured
experimentally due to the phase locking between the two beams. We study the
influence of the waveplate on the various criteria characterizing quantum
correlations. We show in particular that the quantum correlations can be
maximized by using optimized quadratures.Comment: to be published in Eur. Phys. J.
Synchronization of Sound Sources
Sound generation and -interaction is highly complex, nonlinear and
self-organized. Already 150 years ago Lord Rayleigh raised the following
problem: Two nearby organ pipes of different fundamental frequencies sound
together almost inaudibly with identical pitch. This effect is now understood
qualitatively by modern synchronization theory (M. Abel et al., J. Acoust. Soc.
Am., 119(4), 2006). For a detailed, quantitative investigation, we substituted
one pipe by an electric speaker. We observe that even minute driving signals
force the pipe to synchronization, thus yielding three decades of
synchronization -- the largest range ever measured to our knowledge.
Furthermore, a mutual silencing of the pipe is found, which can be explained by
self-organized oscillations, of use for novel methods of noise abatement.
Finally, we develop a specific nonlinear reconstruction method which yields a
perfect quantitative match of experiment and theory.Comment: 5 pages, 4 figure
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