5,675 research outputs found
Robustness of bipartite Gaussian entangled beams propagating in lossy channels
Subtle quantum properties offer exciting new prospects in optical
communications. Quantum entanglement enables the secure exchange of
cryptographic keys and the distribution of quantum information by
teleportation. Entangled bright beams of light attract increasing interest for
such tasks, since they enable the employment of well-established classical
communications techniques. However, quantum resources are fragile and undergo
decoherence by interaction with the environment. The unavoidable losses in the
communication channel can lead to a complete destruction of useful quantum
properties -- the so-called "entanglement sudden death". We investigate the
precise conditions under which this phenomenon takes place for the simplest
case of two light beams and demonstrate how to produce states which are robust
against losses. Our study sheds new light on the intriguing properties of
quantum entanglement and how they may be tamed for future applications.Comment: To be published - Nature Photonic
Integral Field Spectroscopy of two radio galaxies at z~2.3
In this article we study the morphology, kinematics and ionization properties
of the giant ionized gas nebulae surrounding two high redshift radio galaxies,
4C40.36 (z=2.27) and 4C48.48 (z=2.34).}{Integral Field Spectroscopy
observations were taken using the PPAK bundle of the PMAS spectrograph, mounted
on the 3.5m on the Calar Alto Observatory, in order to cover a field-of-view of
64" X 72" centered in each radio galaxy. The observations spanned over 5
nights, using two different spectral resolutions (with FWHM~4 AA and ~8 AA
respectively), covering the optical wavelength range from ~3700 AA to ~7100 AA,
which corresponds to the rest-frame ultraviolet range from ~1100 AA to ~2000 AA
>. Various emission lines are detected within this wavelength range, including
Lyalpha (1216 AA), NV (1240 AA), CIV (1549 AA), HeII (1640 AA), OIII] (1663 AA)
and CIII] (1909\AA). The dataset was used to derive the spatial distribution of
the flux intensity of each of these lines and the gas kinematics. The
properties of the emission lines in the nuclear regions were studied in
detail.In agreement with previous studies, we find that both objects are
embedded in a large ionized gas nebula, where Ly alpha emission is extended
across ~100 kpc or more. The CIV and HeII emission lines are also spatially
extended. The nebulae are generally aligned with the radio axis, although we
detect emission far from it. In 4C+48.48, there is a band of low Ly-alpha/CIV
running perpendicular to the radio axis, at the location of the active nucleus.
This feature might be the observational signature of an edge-on disk of neutral
gas. The kinematics of both nebulae are inconsistent with stable rotation,
although they are not inconsistent with infall or outflow.Comment: 14 pages, 5 figures, accepted for publishing in Astronomy &
Astrophysic
VIMOS-VLT spectroscopy of the giant Ly-alpha nebulae associated with three z~2.5 radio galaxies
The morphological and spectroscopic properties of the giant (>60 kpc)
Ly-alpha nebulae associated with three radio galaxies at z~2.5 (MRC 1558-003,
MRC 2025-218 and MRC 0140-257) have been investigated using integral field
spectroscopic data obtained with VIMOS on VLT.
The morphologies are varied. The nebula of one source has a centrally peaked,
rounded appearance. In the other two objects, it consists of two spatial
components. The three nebulae are aligned with the radio axis within <30 deg.
The total Ly-alpha luminosities are in the range (0.3-3.4) x 1e44 erg s-1. The
Ly-alpha spectral profile shows strong variation through the nebulae, with FWHM
values in the range ~400-1500 km s-1 and velocity shifts V~120-600 km s-1.
We present an infall model which can explain successfully most Ly-alpha
morphological and spectroscopic properties of the nebula associated with MRC
1558-003. This adds further support to our previous conclusion that the
_quiescent_ giant nebulae associated with this and other high redshift powerful
radio galaxies are in infall. A problem for this model is the difficulty to
reproduce the large Ly-alpha FWHM values.
We have discovered a giant (~85 kpc) Ly-alpha nebula associated with the
radio galaxy MRC 0140-257 at z=2.64. It shows strikingly relaxed kinematics
(FWHM2) radio galaxies.Comment: 14 pages, 13 figures. Accepted for publication in MNRA
Disentanglement in Bipartite Continuous-Variable Systems
Entanglement in bipartite continuous-variable systems is investigated in the
presence of partial losses, such as those introduced by a realistic quantum
communication channel, e.g. by propagation in an optical fiber. We find that
entanglement can vanish completely for partial losses, in a situa- tion
reminiscent of so-called entanglement sudden death. Even states with extreme
squeezing may become separable after propagation in lossy channels. Having in
mind the potential applications of such entangled light beams to optical
communications, we investigate the conditions under which entanglement can
survive for all partial losses. Different loss scenarios are examined and we
derive criteria to test the robustness of entangled states. These criteria are
necessary and sufficient for Gaussian states. Our study provides a framework to
investigate the robustness of continuous-variable entanglement in more complex
multipartite systems.Comment: Phys. Rev. A (in press
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