1,786 research outputs found
Proposal for high-precision Atomic Parity Violation measurements using amplification of the asymmetry by stimulated emission in a transverse E and B field pump-probe experiment
Amplification by stimulated emission of radiation provides an intriguing
means for increasing the sensitivity of Atomic Parity Violation (APV)
measurements in a pump-probe configuration well adapted to the 6S-7S cesium
transition. It takes advantage of the large number of atoms excited along the
path of the pump beam. In the longitudinal E-field configuration currently
exploited in an ongoing APV measurement, this number is limited only by the
total voltage sustainable by the Cs vapor. In order to overcome this limit, we
consider, both theoretically and experimentally, the possibility of performing
the measurements in a transverse E-field configuration requiring a much lower
voltage. We discuss the necessarily different nature of the observable and the
magnetoelectric optical effects entering into play. They condition
modifications of the experimental configuration with, in particular, the
application of a transverse magnetic field. We suggest the possibility of
rotating the transverse direction of the fields so as to suppress systematic
effects. With a long interaction length, a precision reaching 0.1 percent in a
quantum noise limited measurement can be expected, now limited only by the
necessity of operating below the threshold of spontaneous superradiant emission
of the excited medium. If we approached this limit, however, we could greatly
amplify the asymmetry using triggered superradiance.Comment: Articl
Pump-probe measurement of atomic parity violation in caesium with a precision of 2.6%
We present the atomic parity violation measurements made in Cs vapour using a
pump-probe scheme. After pulsed excitation of the 6S-7S forbidden transition in
the presence of a longitudinal electric field, a laser beam resonant with one
of the 7S-6P transitions stimulates the 7S atom emission for a duration of 20
ns. The polarisation of the amplified probe beam is analysed. A seven-fold
signature allows discrimination of the parity violating linear dichroism, and
real-time calibration by a similar, known, parity conserving linear dichroism.
The zero-field linear dichroism signal due to the magnetic dipole transition
moment is observed for the first time, and used for in-situ determination of
the electric field. The result, ImE1^{pv}= (-808+/- 21) 10^{-14} ea\_{0}, is in
perfect agreement with the corresponding, more precise measurement obtained by
the Boulder group. A transverse field configuration with large probe
amplification could bring atomic parity violation measurements to the 0.1%
accuracy level.Comment: "conference PAVI 06, Milos, Greece, May 2006
An Atomic Linear Stark Shift Violating P But Not T Arising From the Electroweak Nuclear Anapole Moment
We propose a direct method of detection of the nuclear anapole moment. It is
based on the existence of a linear Stark shift for alkali atoms in their ground
state perturbed by a quadrupolar interaction potential and a magnetic field.
This shift is proportional to the T-even pseudoscalar built from the
quadrupolar potential symmetry axis, the directions of the applied electric and
magnetic fields.It involves on the one hand the anisotropy of the hyperfine
interaction induced by the quadrupolar interaction and, on the other,the static
electric dipole moment arising from electroweak interactions inside the
nucleus. The case of ground state cesium atoms trapped in a uniaxial (hcp)
phase of solid helium-4 is examined. From an explicit evaluation of both the
hyperfine structure anisotropy and the static P-odd T-even dipole deduced from
recent empirical data about the cesium nuclear anapole moment, we predict the
Stark shift. It is three times the experimental upper bound to be set on the
T-odd Stark shift of free cesium atoms in order to improve the present limit on
the electron EDM.Comment: 31 pages, 3 PostScript figure
Atomic interferometer measurements of Berry's and Aharonov-Anandan's phases for isolated spins S > 1/2 non-linearly coupled to external fields
The aim of the present paper is to propose experiments for observing the
significant features of Berry's phases for S>1, generated by spin-Hamiltonians
endowed with two couplings, a magnetic dipole and an electric quadrupole one
with external B and E fields, as theoretically studied in our previous work.
The fields are assumed orthogonal, this mild restriction leading to geometric
and algebraic simplifications. Alkali atoms appear as good candidates for
interferometric measurements but there are challenges to be overcome. The only
practical way to generate a suitable E-field is to use the ac Stark effect
which induces an instability of the dressed atom. Besides atom loss, this might
invalidate Berry's phase derivation but this latter problem can be solved by an
appropriate detuning. The former puts an upper limit to the cycle duration,
which is bounded below by the adiabatic condition. By relying upon our previous
analysis of the non-adiabatic corrections, we have been able to reach a
compromise for the Rb hf level F=2, m=0 state, which is our candidate
for an interferometric measurement of the exotic Berry's phase generated by a
rotation of the E-field around the fixed B-field. By a numerical simulation we
have shown that the non-adiabatic corrections can be kept below the 0.1% level.
As an alternative candidate, we discuss the chromium ground state J=S=3, where
the instability problem is easily solved. We make a proposal to extend the
measurement of Aharonov-Anandan's phase beyond S=1/2 to the Rb hf level
F=m=1, by constructing, with the help of light-shifts, a Hamiltonian able to
perform a parallel transport along a closed circuit upon the density matrix
space, without any adiabatic constraint. In Appendix A, Berry's phase
difference for S=3/2 and 1/2, m=1/2 states is used to perform an entanglement
of 3 Qbits.Comment: 23 pages, 6 figures, modifications in the introduction, two
paragraphs adde
Measurement of the parity violating 6S-7S transition amplitude in cesium achieved within 2 \times 10^{-13} atomic-unit accuracy by stimulated-emission detection
We exploit the process of asymmetry amplification by stimulated emission
which provides an original method for parity violation (PV) measurements in a
highly forbidden atomic transition. The method involves measurements of a
chiral, transient, optical gain of a cesium vapor on the 7S-6P_{3/2}
transition, probed after it is excited by an intense, linearly polarized,
collinear laser, tuned to resonance for one hyperfine line of the forbidden
6S-7S transition in a longitudinal electric field. We report here a 3.5 fold
increase, of the one-second-measurement sensitivity, and subsequent reduction
by a factor of 3.5 of the statistical accuracy compared with our previous
result [J. Gu\'ena et al., Phys. Rev. Lett. 90, 143001 (2003)]. Decisive
improvements to the set-up include an increased repetition rate, better
extinction of the probe beam at the end of the probe pulse and, for the first
time to our knowledge, the following: a polarization-tilt magnifier,
quasi-suppression of beam reflections at the cell windows, and a Cs cell with
electrically conductive windows. We also present real-time tests of systematic
effects, consistency checks on the data, as well as a 1% accurate measurement
of the electric field seen by the atoms, from atomic signals. PV measurements
performed in seven different vapor cells agree within the statistical error.
Our present result is compatible with the more precise Boulder result within
our present relative statistical accuracy of 2.6%, corresponding to a 2 \times
10^{-13} atomic-unit uncertainty in E_1^{pv}. Theoretical motivations for
further measurements are emphasized and we give a brief overview of a recent
proposal that would allow the uncertainty to be reduced to the 0.1% level by
creating conditions where asymmetry amplification is much greater.Comment: Article 21 pages, 6 figures, 3 tables Typos, addition of few comments
and little more data (1 week) leading to a slight reduction of the error bar
Accepted for publication in Phys.Rev.
A new Manifestation of Atomic Parity Violation in Cesium: a Chiral Optical Gain induced by linearly polarized 6S-7S Excitation
We have detected, by using stimulated emission, an Atomic Parity Violation
(APV) in the form of a chiral optical gain of a cesium vapor on the 7S -
6P transition,consecutive to linearly polarized 6S-7S excitation. We
demonstrate the validity of this detection method of APV, by presenting a 9%
accurate measurement of expected sign and magnitude. We underline several
advantages of this entirely new approach in which the cylindrical symmetry of
the set-up can be fully exploited. Future measurements at the percent level
will provide an important cross-check of an existing more precise result
obtained by a different method.Comment: 4 pages, 2 figure
Spatial Constraint Corrections to the Elasticity of dsDNA Measured with Magnetic Tweezers
In this paper, we have studied, within a discrete WLC model, the spatial
constraints in magnetic tweezers used in single molecule experiments. Two
elements are involved: first, the fixed plastic slab on which is stuck the
initial strand, second, the magnetic bead which pulls (or twists) the attached
molecule free end. We have shown that the bead surface can be replaced by its
tangent plane at the anchoring point, when it is close to the bead south pole
relative to the force. We are led to a model with two parallel repulsive
plates: the fixed anchoring plate and a fluctuating plate, simulating the bead,
in thermal equilibrium with the system. The bead effect is a slight upper shift
of the elongation, about four times smaller than the similar effect induced by
the fixed plate. This rather unexpected result, has been qualitatively
confirmed within the soluble Gaussian model. A study of the molecule elongation
versus the countour length exhibits a significant non-extensive behaviour. The
curve for short molecules (with less than 2 kbp) is well fitted by a straight
line, with a slope given by the WLC model, but it does not go through the
origin. The non-extensive offset gives a 15% upward shift to the elongation of
a 2 kbp molecule stretched by a 0.3 pN force.Comment: 28 pages, 6 figures An explanatory figure has been added. The
physical interpretation of the results has been made somewhat more
transparen
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