460 research outputs found
Short term X-ray spectral variability of the quasar PDS 456 observed in a low flux state
We present an analysis of the 2013 Suzaku campaign on the nearby luminous
quasar PDS 456, covering a total duration of ~1 Ms and a net exposure of 455
ks. During these observations, the X-ray flux was suppressed by a factor of >10
in the soft X-ray band when compared to other epochs. We investigated the
broadband continuum by constructing a spectral energy distribution, making use
of the optical/UV photometry and hard X-ray spectra from the later
XMM-Newton/NuSTAR campaign in 2014. The high energy part of this low flux state
cannot be accounted for by self-consistent accretion disc and corona models
without attenuation by absorbing gas, which partially covers a substantial
fraction of the line of sight towards the X-ray source. Two absorption layers
are required, of column density and ,
with average covering factors of ~80% (with typical 5% variations) and 60%
(10-15%), respectively. In these observations PDS 456 displays significant
short term X-ray spectral variability, on timescales of ~100 ks, which can be
accounted for by variable covering of the absorbing gas. The partial covering
absorber prefers an outflow velocity of at
the >99.9% confidence level over the case where . This is
consistent with the velocity of the highly ionised outflow responsible for the
blueshifted iron K absorption profile. We therefore suggest that the partial
covering clouds could be the denser, or clumpy part of an inhomogeneous
accretion disc wind. Finally we estimate the size-scale of the X-ray source
from its variability. The radial extent of the X-ray emitter is found to be of
the order ~15-20 , although the hard X-ray (>2 keV) emission may
originate from a more compact or patchy corona of hot electrons, which is ~6-8
in size.Comment: 38 pages, 13 figures, accepted for publication in MNRA
Scheme for teleportation of quantum states onto a mechanical resonator
We propose an experimentally feasible scheme to teleport an unkown quantum
state onto the vibrational degree of freedom of a macroscopic mirror. The
quantum channel between the two parties is established by exploiting radiation
pressure effects.Comment: 5 pages, 2 figures, in press on PR
Quantum State Reconstruction of a Bose-Einstein Condensate
We propose a tomographic scheme to reconstruct the quantum state of a
Bose-Einstein condensate, exploiting the radiation field as a probe and
considering the atomic internal degrees of freedom. The density matrix in the
number state basis can be directly retrieved from the atom counting
probabilities.Comment: 11 pages, LaTeX file, no figures, to appear in Europhysics Letter
Interference effects in f-deformed fields
We show how the introduction of an algeabric field deformation affects the
interference phenomena. We also give a physical interpretation of the developed
theory.Comment: 6 pages, Latex file, no figures, accepted by Physica Script
Optomechanical sideband cooling of a thin membrane within a cavity
We present an experimental study of dynamical back-action cooling of the
fundamental vibrational mode of a thin semitransparent membrane placed within a
high-finesse optical cavity. We study how the radiation pressure interaction
modifies the mechanical response of the vibrational mode, and the experimental
results are in agreement with a Langevin equation description of the coupled
dynamics. The experiments are carried out in the resolved sideband regime, and
we have observed cooling by a factor 350 We have also observed the mechanical
frequency shift associated with the quadratic term in the expansion of the
cavity mode frequency versus the effective membrane position, which is
typically negligible in other cavity optomechanical devices.Comment: 15 pages, 7 figure
Size effects in ruthenium-based thick-film resistors: rutile vs. pyrochlore-based resistors
The size effect, namely the change of sheet resistance, R, as a function of resistor length, has been investigated in layers whose conductive phase evoves from Pb-rich (Ru-deficient pyrochlores) to Pb2Ru2O6.5 and finally to RuO2 by increasing the firing temperature. It is found that Bi diffusion from the terminations is responsible for lower sheet resistance values in shorter resistors whatever the conductive phase is. On the contrary, Ag diffusion is responsible for lower sheet resistance values in shorte resistors only in the case of ruthenate conductive grains while the reverse is observed in RuO2-based layers. Size effect can be suppressed with Pt/Au-based terminations provided that Bi is contained and with Au-metallorganic-based contact provided that the peak firing temperature is not too high
Motional Squashed States
We show that by using a feedback loop it is possible to reduce the
fluctuations in one quadrature of the vibrational degree of freedom of a
trapped ion below the quantum limit. The stationary state is not a proper
squeezed state, but rather a ``squashed'' state, since the uncertainty in the
orthogonal quadrature, which is larger than the standard quantum limit, is
unaffected by the feedback action.Comment: 8 pages, 2 figures, to appear in the special Issue "Quantum
Correlations and Fluctuations" of J. Opt.
Performance of a deterministic source of entangled photonic qubits
We study the possible limitations and sources of decoherence in the scheme
for the deterministic generation of polarization-entangled photons, recently
proposed by Gheri et al. [K. M. Gheri et al., Phys. Rev. A 58, R2627 (1998)],
based on an appropriately driven single atom trapped within an optical cavity.
We consider in particular the effects of laser intensity fluctuations, photon
losses, and atomic motion.Comment: 10 pages, 6 figure
- …