73 research outputs found
Electron density distribution and solar plasma correction of radio signals using MGS, MEX and VEX spacecraft navigation data and its application to planetary ephemerides
The Mars Global Surveyor (MGS), Mars Express (MEX), and Venus Express (VEX)
experienced several superior solar conjunctions. These conjunctions cause
severe degradations of radio signals when the line of sight between the Earth
and the spacecraft passes near to the solar corona region. The primary
objective of this work is to deduce a solar corona model from the spacecraft
navigation data acquired at the time of solar conjunctions and to estimate its
average electron density. The corrected or improved data are then used to fit
the dynamical modeling of the planet motions, called planetary ephemerides. We
analyzed the radio science raw data of the MGS spacecraft using the orbit
determination software GINS. The range bias, obtained from GINS and provided by
ESA for MEX and VEX, are then used to derive the electron density profile.
These profiles are obtained for different intervals of solar distances: from
12Rs to 215Rs for MGS, 6Rs to 152Rs for MEX, and form 12Rs to 154Rs for VEX.
They are acquired for each spacecraft individually, for ingress and egress
phases separately and both phases together, for different types of solar winds
(fast, slow), and for solar activity phases (minimum, maximum). We compared our
results with the previous estimations that were based on in situ measurements,
and on solar type III radio and radio science studies made at different phases
of solar activity and at different solar wind states. Our results are
consistent with estimations obtained by these different methods. Moreover,
fitting the planetary ephemerides including complementary data that were
corrected for the solar corona perturbations, noticeably improves the
extrapolation capability of the planetary ephemerides and the estimation of the
asteroids masses.Comment: Accepted for publication in A&
Towards continuous-wave regime teleportation for light matter quantum relay stations
We report a teleportation experiment involving narrowband entangled photons
at 1560 nm and qubit photons at 795 nm emulated by faint laser pulses. A
nonlinear difference frequency generation stage converts the 795 nm photons to
1560 nm in order to enable interference with one photon out of the pairs, i.e.,
at the same wavelength. The spectral bandwidth of all involved photons is of
about 25 MHz, which is close to the emission bandwidth of emissive quantum
memory devices, notably those based on ensembles of cold atoms and rare earth
ions. This opens the route towards the realization of hybrid quantum nodes,
i.e., combining quantum memories and entanglement-based quantum relays
exploiting either a synchronized (pulsed) or asynchronous (continuous- wave)
scenario
Polarization entangled photon-pair source based on quantum nonlinear photonics and interferometry
We present a versatile, high-brightness, guided-wave source of polarization
entangled photons, emitted at a telecom wavelength. Photon-pairs are generated
using an integrated type-0 nonlinear waveguide, and subsequently prepared in a
polarization entangled state via a stabilized fiber interferometer. We show
that the single photon emission wavelength can be tuned over more than 50 nm,
whereas the single photon spectral bandwidth can be chosen at will over more
than five orders of magnitude (from 25 MHz to 4 THz). Moreover, by performing
entanglement analysis, we demonstrate a high degree of control of the quantum
state via the violation of the Bell inequalities by more than 40 standard
deviations. This makes this scheme suitable for a wide range of quantum optics
experiments, ranging from fundamental research to quantum information
applications. We report on details of the setup, as well as on the
characterization of all included components, previously outlined in F. Kaiser
et al. (2013 Laser Phys. Lett. 10, 045202).Comment: 16 pages, 7 figure
A versatile source of polarisation entangled photons for quantum network applications
We report a versatile and practical approach for generating high-quality
polarization entanglement in a fully guided-wave fashion. Our setup relies on a
high-brilliance type-0 waveguide generator producing paired photon at a telecom
wavelength associated with an advanced energy-time to polarisation transcriber.
The latter is capable of creating any pure polarization entangled state, and
allows manipulating single photon bandwidths that can be chosen at will over
five orders of magnitude, ranging from tens of MHz to several THz. We achieve
excellent entanglement fidelities for particular spectral bandwidths, i.e. 25
MHz, 540 MHz and 100 GHz, proving the relevance of our approach. Our scheme
stands as an ideal candidate for a wide range of network applications, ranging
from dense division multiplexing quantum key distribution to heralded optical
quantum memories and repeaters.Comment: 5 figure
Polarization entangled photon-pair source based on a type-II PPLN waveguide emitting at a telecom wavelength
We report the realization of a fiber coupled polarization entangled
photon-pair source at 1310 nm based on a birefringent titanium in-diffused
waveguide integrated on periodically poled lithium niobate. By taking advantage
of a dedicated and high-performance setup, we characterized the quantum
properties of the pairs by measuring two-photon interference in both
Hong-Ou-Mandel and standard Bell inequality configurations. We obtained, for
the two sets of measurements, interference net visibilities reaching nearly
100%, which represent important and competitive results compared to similar
waveguide-based configurations already reported. These results prove the
relevance of our approach as an enabling technology for long-distance quantum
communication.Comment: 13 pages, 4 figures, to appear in New Journal of Physic
High-quality polarization entanglement state preparation and manipulation in standard telecommunication channels
We report a novel and simple approach for generating near-perfect quality
polarization entanglement in a fully guided-wave fashion. Both deterministic
pair separation into two adjacent telecommunication channels and the paired
photons' temporal walk-off compensation are achieved using standard fiber
components. Two-photon interference experiments are performed, both for
quantitatively demonstrating the relevance of our approach, and for
manipulating the produced state between bosonic and fermionic symmetries. The
compactness, versatility, and reliability of this configuration makes it a
potential candidate for quantum communication applications.Comment: 6 figure
Analysis of Elliptically Polarized Maximally Entangled States for Bell Inequality Tests
When elliptically polarized maximally entangled states are considered, i.e.,
states having a non random phase factor between the two bipartite polarization
components, the standard settings used for optimal violation of Bell
inequalities are no longer adapted. One way to retrieve the maximal amount of
violation is to compensate for this phase while keeping the standard Bell
inequality analysis settings. We propose in this paper a general theoretical
approach that allows determining and adjusting the phase of elliptically
polarized maximally entangled states in order to optimize the violation of Bell
inequalities. The formalism is also applied to several suggested experimental
phase compensation schemes. In order to emphasize the simplicity and relevance
of our approach, we also describe an experimental implementation using a
standard Soleil-Babinet phase compensator. This device is employed to correct
the phase that appears in the maximally entangled state generated from a
type-II nonlinear photon-pair source after the photons are created and
distributed over fiber channels.Comment: 8 page
Wind/WAVES observations of Auroral Kilometric Radiation: automated burst detection and Terrestrial Solar Wind - Magnetosphere coupling effects
Auroral Kilometric Radiation (AKR) is the strongest terrestrial radio emission, and emanates from the same electron acceleration regions from which particles precipitate into the ionosphere, exciting the aurorae and other phenomena. As such, AKR is a barometer for the state of solar wind - magnetosphere - ionosphere coupling. AKR is anisotropically beamed in a hollow cone from a source region generally found at nightside local times, meaning that a single source region cannot be viewed from all local times in the magnetosphere. In radio data such as dynamic spectra, AKR is frequently observed simultaneously to other radio emissions which can have a similar intensity and frequency range, making it difficult to automatically detect. Building on a previously published pipeline to extract AKR emissions from Wind/WAVES data, in this paper a novel automated AKR burst detection technique is presented and applied again to Wind/WAVES data. Over a five year interval, about 5000 AKR bursts are detected with median burst length ranging from about 30-60 minutes. During detected burst windows, higher solar wind velocity is observed, and the interplanetary magnetic field (IMF) clock angle is observed to tend towards BZ<0, BY<0, when compared with the entire statistical interval. Additionally, higher geomagnetic activity is observed during burst windows at polar, high and equatorial latitudes
Measuring Solar Abundances
This is the rapporteur paper of Working Group 2 on Measuring Solar Abundances. The working group presented and discussed the different observations and methods for obtaining the elemental and isotopic composition of the Sun, and critically reviewed their results and the accuracies thereof. Furthermore, a few important yet unanswered questions were identified, and the potential of future missions to provide answers was assessed
A transonic collisionless model of the solar wind
Because of the semi-collisional nature of the solar wind, the collisionless
or exospheric approach as well as the hydrodynamic one are both inaccurate.
However, the advantage of simplicity makes them useful for enlightening some
basic mechanisms of solar wind acceleration. Previous exospheric models have
been able to reproduce winds that were already nearly supersonic at the
exobase, the altitude above which there are no collisions. In order to allow
transonic solutions, a lower exobase has to be considered, in which case the
protons are experiencing a non-monotonic potential energy profile. This is done
in the present work. In this model, the electron velocity distribution in the
corona is assumed non-thermal. Parametric results are presented and show that
the high acceleration obtained does not depend on the details of the
non-thermal distributions. This acceleration seems, therefore, to be a robust
result produced by the presence of a sufficient number of suprathermal
electrons. A method for improving the exospheric description is also given,
which consists in mapping particle orbits in terms of their invariants of
motion.Comment: 18 pages, 18 figures, accepted for publication in The Astrophysical
Journal (1 May 2004
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