428 research outputs found
Reduction of quantum noise in optical interferometers using squeezed light
We study the photon counting noise in optical interferometers used for
gravitational wave detection. In order to reduce quantum noise a squeezed
vacuum state is injected into the usually unused input port. Here, we
specifically investigate the so called `dark port case', when the beam splitter
is oriented close to 90{\deg} to the incoming laser beam, such that nearly all
photons go to one output port of the interferometer, and only a small fraction
of photons is seen in the other port (`dark port'). For this case it had been
suggested that signal amplification is possible without concurrent noise
amplification [R.Barak and Y.Ben-Aryeh, J.Opt.Soc.Am.B25(361)2008]. We show
that by injection of a squeezed vacuum state into the second input port,
counting noise is reduced for large values of the squeezing factor, however the
signal is not amplified. Signal strength only depends on the intensity of the
laser beam.Comment: 8 pages, 1 figur
The large system asymptotics of persistent currents in mesoscopic quantum rings
We consider a one-dimensional mesoscopic quantum ring filled with spinless
electrons and threaded by a magnetic flux, which carries a persistent current
at zero temperature. The interplay of Coulomb interactions and a single on-site
impurity yields a non-trivial dependence of the persistent current on the size
of the ring. We determine numerically the asymptotic power law for systems up
to 32000 sites for various impurity strengths and compare with predictions from
Bethe Ansatz solutions combined with Bosonization. The numerical results are
obtained using an improved functional renormalization group (fRG) method. We
apply the density matrix renormalization group (DMRG) and exact diagonalization
methods to benchmark the fRG calculations. We use DMRG to study the persistent
current at low electron concentrations in order to extend the validity of our
results to quasi-continuous systems. We briefly comment on the quality of
calculated fRG ground state energies by comparison with exact DMRG data.Comment: REVTex, 12 pages, 12 figs, accepted in Phys. Rev.
Theoretical study of the dynamic structure factor of superfluid 4He
We study the dynamic structure factor of superfluid 4He
at zero temperature in the roton momentum region and beyond using
field-theoretical Green's function techniques. We start from the
Gavoret-Nozi\`{e}res two-particle propagator and introduce the concept of
quasiparticles. We treat the residual (weak) interaction between quasiparticles
as being local in coordinate space and weakly energy dependent. Our
quasiparticle model explicitly incorporates the Bose-Einstein condensate. A
complete formula for the dynamic susceptibility, which is related to , is derived. The structure factor is numerically calculated
in a self-consistent way in the special case of a momentum independent
interaction between quasiparticles. Results are compared with experiment and
other theoretical approaches.Comment: 17 pages, 16 figure
Radiative decays of decuplet hyperons
We calculate the radiative decay widths of decuplet hyperons in a chiral
constituent quark model including electromagnetic exchange currents between
quarks. Exchange currents contribute significantly to the E2 transition
amplitude, while they largely cancel for the M1 transition amplitude.
Strangeness suppression of the radiative hyperon decays is found to be weakened
by exchange currents. Differences and similarities between our results and
other recent model predictions are discussed.Comment: 11 pages, 1 eps figure, revtex, accepted for publication in Phys.
Rev.
Nucleon Polarizabilities from Deuteron Compton Scattering within a Green's-Function Hybrid Approach
We examine elastic Compton scattering from the deuteron for photon energies
ranging from zero to 100 MeV, using state-of-the-art deuteron wave functions
and NN-potentials. Nucleon-nucleon rescattering between emission and absorption
of the two photons is treated by Green's functions in order to ensure gauge
invariance and the correct Thomson limit. With this Green's-function hybrid
approach, we fulfill the low-energy theorem of deuteron Compton scattering and
there is no significant dependence on the deuteron wave function used.
Concerning the nucleon structure, we use Chiral Effective Field Theory with
explicit \Delta(1232) degrees of freedom within the Small Scale Expansion up to
leading-one-loop order. Agreement with available data is good at all energies.
Our 2-parameter fit to all elastic data leads to values for the
static isoscalar dipole polarizabilities which are in excellent agreement with
the isoscalar Baldin sum rule. Taking this value as additional input, we find
\alpha_E^s= (11.3+-0.7(stat)+-0.6(Baldin)) x 10^{-4} fm^3 and \beta_M^s =
(3.2-+0.7(stat)+-0.6(Baldin)) x 10^{-4} fm^3 and conclude by comparison to the
proton numbers that neutron and proton polarizabilities are essentially the
same.Comment: 47 pages LaTeX2e with 20 figures in 59 .eps files, using graphicx.
Minor modifications; extended discussion of theoretical uncertainties of
polarisabilities extraction. Version accepted for publication in EPJ
Morfologia y biologia de Bostryx conspersus (Sowerby) (Mollusca, Bulimulidae) en las lomas costeras del Peru Central
Analyzing the Effects of Neutron Polarizabilities in Elastic Compton Scattering off He
Motivated by the fact that a polarized He nucleus behaves as an
`effective' neutron target, we examine manifestations of neutron
electromagnetic polarizabilities in elastic Compton scattering from the
Helium-3 nucleus. We calculate both unpolarized and double-polarization
observables using chiral perturbation theory to next-to-leading order
() at energies, , where is
the pion mass. Our results show that the unpolarized differential cross section
can be used to measure neutron electric and magnetic polarizabilities, while
two double-polarization observables are sensitive to different linear
combinations of the four neutron spin polarizabilities.
[Note added in 2018] The qualitative conclusions and analytic formulae
presented in this paper are correct, but several of the numerical results are
wrong: see the erratum posted as arXiv:1804.01206 for further details. A full
suite of corrected numerical results for cross sections and asymmetries can be
found in Margaryan et al., arXiv:1804.00956. They can also be obtained as an
interactive Mathematica notebook by emailing [email protected]: 40 pages, 16 figure
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