111 research outputs found
Magnetometry with entangled atomic samples
We present a theory for the estimation of a scalar or a vector magnetic field
by its influence on an ensemble of trapped spin polarized atoms. The atoms
interact off-resonantly with a continuous laser field, and the measurement of
the polarization rotation of the probe light, induced by the dispersive
atom-light coupling, leads to spin-squeezing of the atomic sample which enables
an estimate of the magnetic field which is more precise than that expected from
standard counting statistics. For polarized light and polarized atoms, a
description of the non-classical components of the collective spin angular
momentum for the atoms and the collective Stokes vectors of the light-field in
terms of effective gaussian position and momentum variables is practically
exact. The gaussian formalism describes the dynamics of the system very
effectively and accounts explicitly for the back-action on the atoms due to
measurement and for the estimate of the magnetic field. Multi-component
magnetic fields are estimated by the measurement of suitably chosen atomic
observables and precision and efficiency is gained by dividing the atomic gas
in two or more samples which are entangled by the dispersive atom-light
interaction.Comment: 8 pages, 11 figure
An astronomical search for evidence of new physics: Limits on gravity-induced birefringence from the magnetic white dwarf RE J0317-853
The coupling of the electromagnetic field directly with gravitational gauge
fields leads to new physical effects that can be tested using astronomical
data. Here we consider a particular case for closer scrutiny, a specific
nonminimal coupling of torsion to electromagnetism, which enters into a
metric-affine geometry of space-time. We show that under the assumption of this
nonminimal coupling, spacetime is birefringent in the presence of such a
gravitational field. This leads to the depolarization of light emitted from
extended astrophysical sources. We use polarimetric data of the magnetic white
dwarf to set strong constraints on the essential coupling
constant for this effect, giving k^2 \lsim (19 {m})^2 .Comment: Statements about Moffat's NGT modified. Accepted for publication in
Phys.Rev.
Measurement of qutrits
We proposed the procedure of measuring the unknown state of the three-level
system - the qutrit, which was realized as the arbitrary polarization state of
the single-mode biphoton field. This procedure is accomplished for the set of
the pure states of qutrits; this set is defined by the properties of SU(2)
transformations, that are done by the polarization transformers.Comment: 9 pages, 9 figure
Stokes Parameters as a Minkowskian Four-vector
It is noted that the Jones-matrix formalism for polarization optics is a
six-parameter two-by-two representation of the Lorentz group. It is shown that
the four independent Stokes parameters form a Minkowskian four-vector, just
like the energy-momentum four-vector in special relativity. The optical filters
are represented by four-by-four Lorentz-transformation matrices. This
four-by-four formalism can deal with partial coherence described by the Stokes
parameters. A four-by-four matrix formulation is given for decoherence effects
on the Stokes parameters, and a possible experiment is proposed. It is shown
also that this Lorentz-group formalism leads to optical filters with a symmetry
property corresponding to that of two-dimensional Euclidean transformations.Comment: RevTeX, 22 pages, no figures, submitted to Phys. Rev.
An analysis of the distribution of background star polarization in dark clouds
The polarization observed for stars background to dark clouds (Bok Globules)
is often used as diagnostic to study the ongoing star formation processes in
these clouds. Such polarization in the optical have been reported for eight
nearby clouds CB3, CB25, CB39, CB52, CB54, CB58, CB62 and CB246 in one of our
previous work (Sen et. al. 2000). With a view to understand the origin of this
polarization, the the present work attempts are made to look for any possible
relation between this observed polarization and other physical parameters in
the cloud (like temperature, turbulence etc.). The observed polarization does
not seem to be clearly related to the dust and gas temperatures (T_d and T_g)
in the cloud as expected from the Davis-Greenstein grain alignment mechanism
(Davis & Greenstein, 1952). However, the average observed polarization p_av
appears to be related to the turbulence delta V (measured by 12CO line width)
by the mathematical relation p_av=2.95exp(-0.24delta V). The possible realtion
between the direction of polarization vector and other physical parameters are
also discussed. For this analysis, in addition to the data on above eight
clouds, the data on CB4 (Kane et. al., 1995) are also included for comparison.Comment: 15 pages, 12 figures, To appear in MNRAS, 200
Jordan-Schwinger map, 3D harmonic oscillator constants of motion, and classical and quantum parameters characterizing electromagnetic wave polarization
In this work we introduce a generalization of the Jauch and Rohrlich quantum
Stokes operators when the arrival direction from the source is unknown {\it a
priori}. We define the generalized Stokes operators as the Jordan-Schwinger map
of a triplet of harmonic oscillators with the Gell-Mann and Ne'eman SU(3)
symmetry group matrices. We show that the elements of the Jordan-Schwinger map
are the constants of motion of the three-dimensional isotropic harmonic
oscillator. Also, we show that generalized Stokes Operators together with the
Gell-Mann and Ne'eman matrices may be used to expand the polarization density
matrix. By taking the expectation value of the Stokes operators in a three-mode
coherent state of the electromagnetic field, we obtain the corresponding
generalized classical Stokes parameters. Finally, by means of the constants of
motion of the classical three-dimensional isotropic harmonic oscillator we
describe the geometric properties of the polarization ellips
Polarized light: production and use
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