42,910 research outputs found
Antibunching in an optomechanical oscillator
We theoretically analyze antibunching of the phonon field in an
optomechanical oscillator employ- ing the membrane-in-the-middle geometry. More
specifically, a single-mode mechanical oscillator is quadratically coupled to a
single-mode cavity field in the regime in which the cavity dissipation is a
dominant source of damping, and adiabatic elimination of the cavity field leads
to an effective cubic nonlinearity for the mechanics. We show analytically in
the weak coupling regime that the mechan- ics displays a chaotic phonon field
for small optomechanical cooperativity, whereas an antibunched single-phonon
field appears for large optomechanical cooperativity. This opens the door to
control of the second-order correlation function of a mechanical oscillator in
the weak coupling regime
Reaction of the chick to one atmosphere of oxygen
Experiment to determine chicken reaction to 100 percent oxygen at atmospheric pressur
Embryo development and chick growth in a helium - oxygen atmosphere
Embryo development and chick growth in helium- oxygen atmospher
Symmetry based determination of space-time functions in nonequilibrium growth processes
We study the space-time correlation and response functions in nonequilibrium
growth processes described by linear stochastic Langevin equations. Exploiting
exclusively the existence of space and time dependent symmetries of the
noiseless part of these equations, we derive expressions for the universal
scaling functions of two-time quantities which are found to agree with the
exact expressions obtained from the stochastic equations of motion. The
usefulness of the space-time functions is illustrated through the investigation
of two atomistic growth models, the Family model and the restricted Family
model, which are shown to belong to a unique universality class in 1+1 and in
2+1 space dimensions. This corrects earlier studies which claimed that in 2+1
dimensions the two models belong to different universality classes.Comment: 18 pages, three figures included, submitted to Phys. Rev.
Ab initio determination of an extended Heisenberg Hamiltonian in CuO2 layers
Accurate ab initio calculations on embedded Cu_4O_{12} square clusters,
fragments of the La_2CuO_4 lattice, confirm a value of the nearest neighbor
antiferromagnetic coupling (J=124 meV) previously obtained from ab initio
calculations on bicentric clusters and in good agreement with experiment. These
calculations predict non negligible antiferromagnetic second-neighbor
interaction (J'=6.5 meV) and four-spin cyclic exchange (K=14 meV), which may
affect the thermodynamic and spectroscopic properties of these materials. The
dependence of the magnetic coupling on local lattice distortions has also been
investigated. Among them the best candidate to induce a spin-phonon effect
seems to be the movement of the Cu atoms, changing the Cu-Cu distance, for
which the variation of the nearest neighbor magnetic coupling with the Cu-O
distance is {\Delta J}/{\Delta d_{Cu-O}}\sim 1700 cm^{-1} A^{-1}.Comment: 11 pages, 5 figures, submitted to Phys. Rev.
Shaping an ultracold atomic soliton in a travelling wave laser beam
An ultracold wave packet of bosonic atoms loaded into a travelling laser wave
may form a many-atom soliton.This is disturbed by a homogeneous force field,
for example by the inevitable gravitation. The wave packet is accelerated and
therefore the laser frequency appears to be chirped in the rest frame of the
atoms. We derive the effective nonlinear Schr\"odinger equation. It shows a
time dependent nonlinearity coefficient which amounts to a damping or
antidamping, respectively. The accelerated packet solution remains a soliton
which changes its shape adiabatically. Similarly, an active shaping can be
obtained in the force-free case by chirping the laser frequency thus
representing a way of coherent control of the soliton form. The experimental
consequences are discussed.Comment: 5 pages, Latex, to published in Europhys. Let
Quantum state transfer between a Bose-Einstein condensate and an optomechanical mirror
In this paper we describe a scheme for state transfer between a trapped
atomic Bose condensate and an optomechanical end-mirror mediated by a cavity
field. Coupling between the mirror and the cold gas arises from the fact that
the cavity field can produce density oscillations in the gas which in turn acts
as an internal Bragg mirror for the field. After adiabatic elimination of the
cavity field we find that the hybrid system of the gas and mirror is described
by a beam splitter Hamiltonian that allows for state transfer, but only if the
quantum nature of the cavity field is retained
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