126 research outputs found
Long-lived quantum memory with nuclear atomic spins
We propose to store non-classical states of light into the macroscopic
collective nuclear spin ( atoms) of a He vapor, using
metastability exchange collisions. These collisions, commonly used to transfer
orientation from the metastable state to the ground state state of
He, can also transfer quantum correlations. This gives a possible
experimental scheme to map a squeezed vacuum field state onto a nuclear spin
state with very long storage times (hours).Comment: 4 page
Efficient atomization of cesium metal in solid helium by low energy (10 J) femtosecond pulses
Metal atoms in solid and liquid helium-4 have attracted some interest either
as a way to keep the atoms in a weakly perturbing matrix, or using them as a
probe for the helium host medium. Laser sputtering with nanosecond pulsed
lasers is the most often used method for atom production, resulting however in
a substantial perturbation of the matrix. We show that a much weaker
perturbation can be obtained by using femtosecond laser pulses with energy as
low as 10 J. As an unexpected benefit, the atomic density produced is much
higher
Observation of metastable hcp solid helium
We have produced and observed metastable solid helium-4 below its melting
pressure between 1.1 K and 1.4 K. This is achieved by an intense pressure wave
carefully focused inside a crystal of known orientation. An accurate density
map of the focal zone is provided by an optical interferometric technique.
Depending on the sample, minimum density achieved at focus corresponds to
pressures between 2 and 4 bar below the static melting pressure. Beyond, the
crystal undergoes an unexpected instability much earlier than the predicted
spinodal limit. This opens a novel opportunity to study this quantum crystal in
an expanded metastable state and its stability limits.Comment: deuxi\`eme versio
Discovery of dumbbell-shaped Cs*He_n exciplexes in solid He 4
We have observed several new spectral features in the fluorescence of cesium
atoms implanted in the hcp phase of solid helium following laser excitation to
the 6P states. Based on calculations of the emission spectra using
semiempirical Cs-He pair potentials the newly discovered lines can be assigned
to the decay of specific Cs*He exciplexes: an apple-shaped CsHe and a dumbbell-shaped CsHe exciplex with
a well defined number of bound helium atoms. While the former has been
observed in other enviroments, it was commonly believed that exciplexes with
might not exist. The calculations suggest CsHe to be
the most probable candidate for that exciplex, in which the helium atoms are
arranged on a ring around the waist of the dumbbell shaped electronic density
distribution of the cesium atom.Comment: 4 pages, 4 figure
Search for anisotropic effects of hcp solid helium on optical lines of cesium impurities
The anisotropic effect of a hcp 4He solid matrix on cesium atoms has been
proposed as a tool to reveal the parity violating anapole moment of its
nucleus. It should also result in splitting the D2 optical excitation line in a
way depending on the light polarization. An experimental investigation has been
set up using oriented hcp helium crystals in which cesium metal grains are
embedded. Atoms are created by laser sputtering from this grains. Optical
absorption spectra of the D2 line have been recorded in the temperature range
of 1.0 to 1.4 K at liquid/solid coexistence pressure by monitoring the
fluorescence on the D2 line at 950 nm. No significant effect of the light
polarization has been found, suggesting a statistically isotropic disordered
solid environment for the cesium atoms.Comment: The original publication will be available at
http://www.springerlink.co
Prewetting transition on a weakly disordered substrate : evidence for a creeping film dynamics
We present the first microscopic images of the prewetting transition of a
liquid film on a solid surface. Pictures of the local coverage map of a helium
film on a cesium metal surface are taken while the temperature is raised
through the transition. The film edge is found to advance at constant
temperature by successive avalanches in a creep motion with a macroscopic
correlation length. The creep velocity varies strongly in a narrow temperature
range. The retreat motion is obtained only at much lower temperature,
conforming to the strong hysteresis observed for prewetting transition on a
disordered surface. Prewetting transition on such disordered surfaces appears
to give rise to dynamical phenomena similar to what is observed for domain wall
motions in 2D magnets.Comment: 7 pages, 3 figures, to be published in Euro.Phys.Let
Optimization and performance of an optical cardio-magnetometer
Cardiomagnetometry is a growing field of noninvasive medical diagnostics that
has triggered a need for affordable high-sensitivity magnetometers. Optical
pumping magnetometers are promising candidates satisfying that need since it
was demonstrated that they can map the heart magnetic field. For the
optimization of such devices theoretical limits on the performance as well as
an experimental approach is presented. The promising result is a intrinsic
magnetometric sensitivity of 63 fT / Hz^1/2 a measurement bandwidth of 140 Hz
and a spatial resolution of 28 mm
Probing vortices in 4He nanodroplets
We present static and dynamical properties of linear vortices in 4He droplets
obtained from Density Functional calculations. By comparing the adsorption
properties of different atomic impurities embedded in pure droplets and in
droplets where a quantized vortex has been created, we suggest that Ca atoms
should be the dopant of choice to detect vortices by means of spectroscopic
experiments.Comment: Typeset using Revtex4, 4 pages and 2 Postscript file
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