227 research outputs found
Precision spectroscopy of the molecular ion HD+: control of Zeeman shifts
Precision spectroscopy on cold molecules can potentially enable novel tests
of fundamental laws of physics and alternative determination of some
fundamental constants. Realizing this potential requires a thorough
understanding of the systematic effects that shift the energy levels of
molecules. We have performed a complete ab initio calculation of the magnetic
field effects for a particular system, the heteronuclear molecular hydrogen ion
HD+. Different spectroscopic schemes have been considered, and numerous
transitions, all accessible by modern radiation sources and exhibiting well
controllable or negligible Zeeman shift, have been found to exist. Thus, HD+ is
a perspective candidate for determination of the ratio of electron-to-nuclear
reduced mass, and for tests of its time-independence.Comment: A Table added, references and figures update
The Cauchy problem on a characteristic cone for the Einstein equations in arbitrary dimensions
We derive explicit formulae for a set of constraints for the Einstein
equations on a null hypersurface, in arbitrary dimensions. We solve these
constraints and show that they provide necessary and sufficient conditions so
that a spacetime solution of the Cauchy problem on a characteristic cone for
the hyperbolic system of the reduced Einstein equations in wave-map gauge also
satisfies the full Einstein equations. We prove a geometric uniqueness theorem
for this Cauchy problem in the vacuum case.Comment: 83 pages, 1 figur
Doppler cooling to the recoil limit using sharp atomic transitions
In this paper, we develop an analytical approach to Doppler cooling of atoms
by one- or two-photon transitions when the natural width of the excited level
is so small that the process leads to a Doppler temperature comparable to the
recoil temperature. A ``quenching'' of the sharp line is introduced in order to
allow control of the time scale of the problem. In such limit, the usual
Fokker-Planck equation does not correctly describe the cooling process. We
propose a generalization of the Fokker-Planck equation and derive a new model
which is able to reproduce correctly the numerical results, up to the recoil
limit. Two cases of practical interest, one-photon Doppler cooling of strontium
and two-photon Doppler cooling of hydrogen are considered.Comment: 5 pages, RevTex 4, submitted to JOSA B (special issue "laser cooling
of atoms"
Continuous-wave Doppler-cooling of hydrogen atoms with two-photon transitions
We propose and analyze the possibility of performing two-photon
continuous-wave Doppler-cooling of hydrogen atoms using the 1S-2S transition.
"Quenching" of the 2S level (by coupling with the 2P state) is used to increase
the cycling frequency, and to control the equilibrium temperature. Theoretical
and numerical studies of the heating effect due to Doppler-free two-photon
transitions evidence an increase of the temperature by a factor of two. The
equilibrium temperature decreases with the effective (quenching dependent)
width of the excited state and can thus be adjusted up to values close to the
recoil temperature.Comment: 11 pages, 4 figures in eps forma
Non-linear spectroscopy of rubidium: An undergraduate experiment
In this paper, we describe two complementary non-linear spectroscopy methods
which both allow to achieve Doppler-free spectra of atomic gases. First,
saturated absorption spectroscopy is used to investigate the structure of the
transition in rubidium. Using a slightly
modified experimental setup, Doppler-free two-photon absorption spectroscopy is
then performed on the transition in
rubidium, leading to accurate measurements of the hyperfine structure of the
energy level. In addition, electric dipole selection rules of
the two-photon transition are investigated, first by modifying the polarization
of the excitation laser, and then by measuring two-photon absorption spectra
when a magnetic field is applied close to the rubidium vapor. All experiments
are performed with the same grating-feedback laser diode, providing an
opportunity to compare different high resolution spectroscopy methods using a
single experimental setup. Such experiments may acquaint students with quantum
mechanics selection rules, atomic spectra and Zeeman effect.Comment: 16 pages, 8 figure
Conformal scattering for a nonlinear wave equation on a curved background
The purpose of this paper is to establish a geometric scattering result for a
conformally invariant nonlinear wave equation on an asymptotically simple
spacetime. The scattering operator is obtained via trace operators at null
infinities. The proof is achieved in three steps. A priori linear estimates are
obtained via an adaptation of the Morawetz vector field in the Schwarzschild
spacetime and a method used by H\"ormander for the Goursat problem. A
well-posedness result for the characteristic Cauchy problem on a light cone at
infinity is then obtained. This requires a control of the nonlinearity uniform
in time which comes from an estimates of the Sobolev constant and a decay
assumption on the nonlinearity of the equation. Finally, the trace operators on
conformal infinities are built and used to define the conformal scattering
operator
Reducing the first-order Doppler shift in a Sagnac interferometer
4p(5)p[1/2](0) transition in Kr at lambda = 212 nm. The achieved precision of 6 x 10(-10) is limited by the characteristics of the laser system. (c) 2007 Optical Society of America
An Improved Experimental Limit on the Electric Dipole Moment of the Neutron
An experimental search for an electric-dipole moment (EDM) of the neutron has
been carried out at the Institut Laue-Langevin (ILL), Grenoble. Spurious
signals from magnetic-field fluctuations were reduced to insignificance by the
use of a cohabiting atomic-mercury magnetometer. Systematic uncertainties,
including geometric-phase-induced false EDMs, have been carefully studied. Two
independent approaches to the analysis have been adopted. The overall results
may be interpreted as an upper limit on the absolute value of the neutron EDM
of |d_n| < 2.9 x 10^{-26} e cm (90% CL).Comment: 5 pages, 2 figures. The published PRL is slightly more terse (e.g. no
section headings) than this version, due to space constraints. Note a small
correction-to-a-correction led to an adjustment of the final limit from 3.0
to 2.9 E-26 e.cm compared to the first version of this preprin
- …