73 research outputs found
Observation of light dragging in rubidium vapor cell
We report on the experimental demonstration of light dragging effect due to
atomic motion in a rubidium vapor cell. We found that the minimum group
velocity is achieved for light red-shifted from the center of the atomic
resonance, and that the value of this shift increases with decreasing group
velocity, in agreement with the theoretical predictions by Kocharovskaya,
Rostovtsev, and Scully [Phys. Rev. Lett. {\bf 86}, 628 (2001)].Comment: 4 pages 4 figures, submitted to PR
A modern Fizeau experiment for education and outreach purposes
On the occasion of the laser's 50th anniversary, we performed a modern Fizeau
experiment, measuring the speed of light with a laser beam passing over the
city centre of Marseille. For a round trip distance of almost five kilometers,
the measurement has reached an uncertainty of about 10, mainly due to
atmospheric fluctuations. We present the experimental and pedagogical
challenges of this brilliant outreach experiment.Comment: accepted by Eur J Phys in november 201
Generalized Sagnac Effect
Experiments were conducted to study light propagation in a light waveguide
loop consisting of linearly and circularly moving segments. We found that any
segment of the loop contributes to the total phase difference between two
counterpropagating light beams in the loop. The contribution is proportional to
a product of the moving velocity v and the projection of the segment length
Deltal on the moving direction, Deltaphi=4pivDeltal/clambda. It is independent
of the type of motion and the refractive index of waveguides. The finding
includes the Sagnac effect of rotation as a special case and suggests a new
fiber optic sensor for measuring linear motion with nanoscale sensitivity.Comment: 3 pages (including 3 figures
Arago (1810): the first experimental result against the ether
95 years before Special Relativity was born, Arago attempted to detect the
absolute motion of the Earth by measuring the deflection of starlight passing
through a prism fixed to the Earth. The null result of this experiment gave
rise to the Fresnel's hypothesis of an ether partly dragged by a moving
substance. In the context of Einstein's Relativity, the sole frame which is
privileged in Arago's experiment is the proper frame of the prism, and the null
result only says that Snell's law is valid in that frame. We revisit the
history of this premature first evidence against the ether theory and calculate
the Fresnel's dragging coefficient by applying the Huygens' construction in the
frame of the prism. We expose the dissimilar treatment received by the ray and
the wave front as an unavoidable consequence of the classical notions of space
and time.Comment: 16 pages. To appear in European Journal of Physic
Imaging and Nulling with the Space Interferometry Mission
We present numerical simulations for a possible synthesis imaging mode of the
Space Interferometer Mission (SIM). We summarize the general techniques that
SIM offers to perform imaging of high surface brightness sources, and discuss
their strengths and weaknesses. We describe an interactive software package
that is used to provide realistic, photometrically correct estimates of SIM
performance for various classes of astronomical objects. In particular, we
simulate the cases of gaseous disks around black holes in the nuclei of
galaxies, and zodiacal dust disks around young stellar objects. Regarding the
first, we show that a Keplerian velocity gradient of the line-emitting gaseous
disk -- and thus the mass of the putative black hole -- can be determined with
SIM to unprecedented accuracy in about 5 hours of integration time for objects
with H_alpha surface brigthness comparable to the prototype M 87. Detections
and observations of exo-zodiacal dust disks depend critically on the disk
properties and the nulling capabilities of SIM. Systems with similar disk size
and at least one tenth of the dust content of beta Pic can be detected by SIM
at distances between 100 pc and a few kpc, if a nulling efficiency of 1/10000
is achieved. Possible inner clear regions indicative of the presence of massive
planets can also be detected and imaged. On the other hand, exo-zodiacal disks
with properties more similar to the solar system will not be found in
reasonable integration times with SIM.Comment: 28 pages, incl. 8 postscript figures, excl. 10 gif-figures Submitted
to Ap
Controllable enhanced dragging of light in ultradispersive media
Article discussing research on the controllable enhanced dragging of light in ultradispersive media
Spin-Orbit Twisted Spin Waves : Group Velocity Control
We present a theoretical and experimental study of the interplay between spin-orbit coupling (SOC), Coulomb interaction, and motion of conduction electrons in a magnetized two-dimensional electron gas. Via a transformation of the many-body Hamiltonian we introduce the concept of spin-orbit twisted spin waves, whose energy dispersions and damping rates are obtained by a simple wave-vector shift of the spin waves without SOC. These theoretical predictions are validated by Raman scattering measurements. With optical gating of the density, we vary the strength of the SOC to alter the group velocity of the spin wave. The findings presented here differ from that of spin systems subject to the Dzyaloshinskii-Moriya interaction. Our results pave the way for novel applications in spin-wave routing devices and for the realization of lenses for spin waves
"Fresnel light drag in a coherently driven moving medium"
We theoretically study how the phase of a light plane wave propagating in a resonant medium under electromagnetically induced transparency (EIT) is affected by the uniform motion of the medium. For cuprous oxide (Cu2O), where EIT can be implemented through a typical pump-probe configuration, the resonant probe beam experiences a phase shift (Fresnel-Fizeau effect) that may vary over a wide range of values, positive or negative, and even vanishing, due to the combined effects of the strong frequency dispersion and anisotropy both induced by the pump. The use of such a coherently driven dragging medium may improve by at least 1 order of magnitude the sensitivity at low velocity in optical drag experiments
Decoherence, fluctuations and Wigner function in neutron optics
We analyze the coherence properties of neutron wave packets, after they have
interacted with a phase shifter undergoing different kinds of statistical
fluctuations. We give a quantitative (and operational) definition of
decoherence and compare it to the standard deviation of the distribution of the
phase shifts. We find that in some cases the neutron ensemble is more coherent,
even though it has interacted with a wider (i.e. more disordered) distribution
of shifts. This feature is independent of the particular definition of
decoherence: this is shown by proposing and discussing an alternative
definition, based on the Wigner function, that displays a similar behavior. We
briefly discuss the notion of entropy of the shifts and find that, in general,
it does not correspond to that of decoherence of the neutron.Comment: 18 pages, 7 figure
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