2,411 research outputs found
Axial range of conjugate adaptive optics in two-photon microscopy
We describe an adaptive optics technique for two-photon microscopy in which
the deformable mirror used for aberration compensation is positioned in a plane
conjugate to the plane of the aberration. We demonstrate in a
proof-of-principle experiment that this technique yields a large field of view
advantage in comparison to standard pupil-conjugate adaptive optics. Further,
we show that the extended field of view in conjugate AO is maintained over a
relatively large axial translation of the deformable mirror with respect to the
conjugate plane. We conclude with a discussion of limitations and prospects for
the conjugate AO technique in two-photon biological microscopy
Planar spin exchange in LiNiO_2
We study the planar spin exchange couplings in LiNiO2 using a perturbative
approach. We show that the inclusion of the trigonal crystal field splitting at
the Oxygen sites leads to the appearance of antiferromagnetic exchange
integrals in deviation from the Goodenough-Kanamori-Anderson rules for this 90
degree bond. That gives a microscopic foundation for the recently observed
coexistence of ferromagnetic and antiferromagnetic couplings in the
orbitally-frustrated state of LiNiO2. (F. Reynaud et al, Phys. Rev. Lett. 86,
3638 (2001))Comment: latex, revtex4, 6 pages, 3 figure
Orbital frustration at the origin of the magnetic behavior in LiNiO2
We report on the ESR, magnetization and magnetic susceptibility measurements
performed over a large temperature range, from 1.5 to 750 K, on high-quality
stoichiometric LiNiO2. We find that this compound displays two distinct
temperature regions where its magnetic behavior is anomalous. With the help of
a statistical model based on the Kugel'-Khomskii Hamiltonian, we show that
below T_of ~ 400 K, an orbitally-frustrated state characteristic of the
triangular lattice is established. This then gives a solution to the
long-standing controversial problem of the magnetic behavior in LiNiO2.Comment: 5 pages, 5 figures, RevTex, accepted in PR
Rev and Rex proteins of human complex retroviruses function with the MMTV Rem-responsive element
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
Mortensen Observer for a class of variational inequalities -Lost equivalence with stochastic filtering approaches
We address the problem of deterministic sequential estimation for a nonsmooth
dynamics in R governed by a variational inequality, as illustrated by the
Skorokhod problem with a reflective boundary condition at 0. For smooth
dynamics, Mortensen introduced an energy for the likelihood that the state
variable produces-up to perturbations disturbances-a given observation in a
finite time interval, while reaching a given target state at the final time.
The Mortensen observer is the minimiser of this energy. For dynamics given by a
variational inequality and therefore not reversible in time, we study the
definition of a Mortensen estimator. On the one hand, we address this problem
by relaxing the boundary constraint of the synthetic variable and then
proposing an approximated variant of the Mortensen estimator that uses the
resulting nonlinear smooth dynamics. On the other hand, inspired by the smooth
dynamics approach, we study the vanishing viscosity limit of the
Hamilton-Jacobi equation satisfied by the Hopf-Cole transform of the solution
of the robust Zakai equation. We prove a stability result that allows us to
interpret the limiting solution as the value function associated with a control
problem rather than an estimation problem. In contrast to the case of smooth
dynamics, here the zero-noise limit of the robust form of the Zakai equation
cannot be understood from the Bellman equation of the value function arising in
Mortensen's deterministic estimation. This may unveil a violation of
equivalence for non-reversible dynamics between the Mortensen approach and the
low noise stochastic approach for nonsmooth dynamics
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
Quantum interference of ultrastable twin optical beams
We report the first measurement of the quantum phase-difference noise of an
ultrastable nondegenerate optical parametric oscillator that emits twin beams
classically phase-locked at exact frequency degeneracy. The measurement
illustrates the property of a lossless balanced beam-splitter to convert
number-difference squeezing into phase-difference squeezing and, thus, provides
indirect evidence for Heisenberg-limited interferometry using twin beams. This
experiment is a generalization of the Hong-Ou-Mandel interference effect for
continuous variables and constitutes a milestone towards continuous-variable
entanglement of bright, ultrastable nondegenerate beams.Comment: 4 pages, 4 figs, accepted by Phys. Rev. Let
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