514 research outputs found
Navigation in Curved Space-Time
A covariant and invariant theory of navigation in curved space-time with
respect to electromagnetic beacons is written in terms of J. L. Synge's
two-point invariant world function. Explicit equations are given for navigation
in space-time in the vicinity of the Earth in Schwarzschild coordinates and in
rotating coordinates. The restricted problem of determining an observer's
coordinate time when their spatial position is known is also considered
Sagnac interference in Carbon nanotube loops
In this paper we study electron interference in nanotube loops. The
conductance as a function of the applied voltage is shown to oscillate due to
interference between electron beams traversing the loop in two opposite
directions, with slightly different velocities. The period of these
oscillations with respect to the gate voltage, as well as the temperatures
required for the effect to appear, are shown to be much larger than those of
the related Fabry-Perot interference. This effect is analogous to the Sagnac
effect in light interferometers. We calculate the effect of interactions on the
period of the oscillations, and show that even though interactions destroy much
of the near-degeneracy of velocities in the symmetric spin channel, the slow
interference effects survive.Comment: 5 pages, 4 figure
On a generalized gravitational Aharonov-Bohm effect
A massless spinor particle is considered in the background gravitational
field due to a rotating body. In the weak field approximation it is shown that
the solution of the Weyl equations depend on the angular momentum of the
rotating body, which does not affect the curvature in this approximation. This
result may be looked upon as a generalization of the gravitational
Aharonov-Bohm effect.Comment: 10 pages, LATEX fil
Sagnac interferometry based on ultra-slow polaritons in cold atomic vapors
The advantages of light and matter-wave Sagnac interferometers -- large area
on one hand and high rotational sensitivity per unit area on the other -- can
be combined utilizing ultra-slow light in cold atomic gases. While a
group-velocity reduction alone does not affect the Sagnac phase shift, the
associated momentum transfer from light to atoms generates a coherent
matter-wave component which gives rise to a substantially enhanced rotational
signal. It is shown that matter-wave sensitivity in a large-area interferometer
can be achieved if an optically dense vapor at sub-recoil temperatures is used.
Already a noticeable enhancement of the Sagnac phase shift is possible however
with much less cooling requirements.Comment: 4 pages, 3 figure
A large magnetic storage ring for Bose-Einstein condensates
Cold atomic clouds and Bose-Einstein condensates have been stored in a 10cm
diameter vertically-oriented magnetic ring. An azimuthal magnetic field enables
low-loss propagation of atomic clouds over a total distance of 2m, with a
heating rate of less than 50nK/s. The vertical geometry was used to split an
atomic cloud into two counter-rotating clouds which were recombined after one
revolution. The system will be ideal for studying condensate collisions and
ultimately Sagnac interferometry.Comment: 4 pages, 5 figure
Triangular Ring Resonator: Direct measurement of the parity-odd parameters of the photon sector of SME
We introduce the the Triangular Ring (TR) resonator. We show that the
difference between the clockwise and anti-clockwise resonant frequencies of a
vacuum TR resonator is sensitive to the birefringence parity-odd parameters of
the photon's sector of the minimal Standard Model Extension (mSME): the
Standard Model plus all the perturbative parameters encoding the break the
Lorentz symmetry. We report that utilizing the current technology allows for
direct measurement of these parameters with a sensitivity of the parity even
ones and improves the best current resonator bounds by couple of orders of
magnitudes.
We note that designing an optical table that rotates perpendicular to the
gravitational equipotential surface (geoid) allows for direct measurement of
the constancy of the light speed at the vicinity of the earth in all directions
in particular perpendicular to the geoid. If this table could achieve the
precision of the ordinary tables, then it would improve the GPS bounds on the
constancy of the light speed perpendicular to geoid by about eight orders of
magnitude.Comment: ref. added, minor corrections, matches the published versio
Modified Sagnac experiment for measuring travel-time difference between counter-propagating light beams in a uniformly moving fiber
A fiber optic conveyor has been developed for investigating the travel-time
difference between two counter-propagating light beams in uniformly moving
fiber. Our finding is that there is a travel-time difference
Deltat=2vDeltal/c^2 in a fiber segment of length Deltal moving with the source
and detector at a speed v, whether the segment is moving uniformly or
circularly.Comment: 4 pages, including 4 figure
Entanglement enhanced atomic gyroscope
The advent of increasingly precise gyroscopes has played a key role in the
technological development of navigation systems. Ring-laser and fibre-optic
gyroscopes, for example, are widely used in modern inertial guidance systems
and rely on the interference of unentangled photons to measure mechanical
rotation. The sensitivity of these devices scales with the number of particles
used as . Here we demonstrate how, by using sources of entangled
particles, it is possible to do better and even achieve the ultimate limit
allowed by quantum mechanics where the precision scales as 1/N. We propose a
gyroscope scheme that uses ultra-cold atoms trapped in an optical ring
potential.Comment: 19 pages, 2 figure
Gravitomagnetism, clocks and geometry
New techniques to evaluate the clock effect using light are described. These
are based on the flatness of the cylindrical surface containing the world lines
of the rays constrained to move on circular trajectories about a spinning mass.
The effect of the angular momentum of the source is manifested in the fact that
inertial observers must be replaced by local non rotating observers. Starting
from this an exact formula for circular trajectories is found. Numerical
estimates for the Earth environment show that light would be a better probe
than actual clocks to evidence the angular momentum influence. The advantages
of light in connection with some principle experiments are shortly reviewed.Comment: TCI Latex, 12 pages, 2 figures. To appear in European Journal of
Physic
Quantum sensitivity limit of a Sagnac hybrid interferometer based on slow-light propagation in ultra-cold gases
The light--matter-wave Sagnac interferometer based on ultra-slow light
proposed recently in (Phys. Rev. Lett. 92, 253201 (2004)) is analyzed in
detail. In particular the effect of confining potentials is examined and it is
shown that the ultra-slow light attains a rotational phase shift equivalent to
that of a matter wave, if and only if the coherence transfer from light to
atoms associated with slow light is associated with a momentum transfer and if
an ultra-cold gas in a ring trap is used. The quantum sensitivity limit of the
Sagnac interferometer is determined and the minimum detectable rotation rate
calculated. It is shown that the slow-light interferometer allows for a
significantly higher signal-to-noise ratio as possible in current matter-wave
gyroscopes.Comment: 12 pages, 6 figure
- …