590 research outputs found
Collision effects in velocity-selective optical pumping of sodium
We report on a quantitative experimental investigation of velocity-changing collisions by means of velocity-selective optical pumping (VSOP). We have calculated the VSOP line shape for an atom with hyperfine structure with the use of two phenomenological kernels for the collision effects: the Keilson-Storer kernel, and a two-term kernel consisting of a broad Keilson-Storer part and a narrower Gaussian component. Corrections were included to account for the finite absorption in the sample and the backward reflection of the pumping beam. The experiments were carried out in sodium vapor with neon as the perturber gas. The D1 line of sodium was used for optical pumping, and the orientation of the ground state was detected. Free parameters of the theory were determined by fitting the predicted line shapes to experimental curves. The Keilson-Storer kernel proved unsatisfactory, but the two-term kernel reproduced well the observed line shapes over the entire collision profiles in the neon pressure range 0-57 mtorr. In an independent experiment using rapidly modulated VSOP we also measured directly the cross section of velocity-changing collisions: σ=(1.13±0.10)×10exp−14 cm2. The large weight obtained for the narrow Gaussian from the fits, as well as the collision cross section which is three times as large as the cross section deduced from tabulated gas kinetic radii, may indicate the presence of collisions with relatively small velocity changes in addition to hard-sphere encounters.Peer reviewe
Spin correlations in the extended kagome system YBaCo3FeO7
The transition metal based oxide YBaCo3FeO7 is structurally related to the
mineral Swedenborgite SbNaBe4O7, a polar non-centrosymmetric crystal system.
The magnetic Co3Fe sublattice consists of a tetrahedral network containing
kagome-like layers with trigonal interlayer sites. This geometry causes
frustration effects for magnetic ordering, which were investigated by
magnetization measurements, M\"ossbauer spectroscopy, polarized neutron
diffraction, and neutron spectroscopy. Magnetization measurement and neutron
diffraction do not show long range ordering even at low temperature (1 K)
although a strong antiferromagnetic coupling (~2000 K) is deduced from the
magnetic susceptibility. Below 590 K, we observe two features, a spontaneous
weak anisotropic magnetization hysteresis along the polar crystallographic axis
and a hyperfine field on the Fe kagome sites, whereas the Fe spins on the
interlayer sites remain idle. Below ~50 K, the onset of a hyperfine field shows
the development of moments static on the M\"ossbauer time scale also for the Fe
interlayer sites. Simultaneously, an increase of spin correlations is found by
polarized neutron diffraction. The relaxation part of the dynamic response has
been further investigated by high-resolution neutron spectroscopy, which
reveals that the spin correlations start to freeze in below ~50 K. Monte Carlo
simulations show that the neutron scattering results at lower temperatures are
compatible with a recent proposal that the particular geometric frustration in
the Swedenborgite structure promotes quasi one dimensional partial order.Comment: 13 pages, 7 figure
High-sensitivity optical measurement of mechanical Brownian motion
We describe an experiment in which a laser beam is sent into a high-finesse
optical cavity with a mirror coated on a mechanical resonator. We show that the
reflected light is very sensitive to small mirror displacements. We have
observed the Brownian motion of the resonator with a very high sensitivity.Comment: 4 pages, 4 figures, RevTe
Structure Determination of Oligosaccharides Isolated from A + , H + and A − H − Hog-Submaxillary-Gland Mucin Glyoproteins, by 360-MHz 1 H-NMR Spectroscopy, Permethylation Analysis and Mass Spectrometry
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65915/1/j.1432-1033.1981.tb05545.x.pd
Transitions between levels of a quantum bouncer induced by a noise-like perturbation
The probability of transition between levels of a quantum bouncer, induced by
a noise-like perturbation, is calculated. The results are applied to two
sources of noise (vibrations and mirror surface waviness) which might play an
important role in future GRANIT experiment, aiming at precision studies of/with
the neutron quantum bouncer
Coherent Evolution of Bouncing Bose-Einstein Condensates
We investigate the evolution of Bose-Einstein condensates falling under
gravity and bouncing off a mirror formed by a far-detuned sheet of light. After
reflection, the atomic density profile develops splitting and interference
structures which depend on the drop height, on the strength of the light sheet,
as well as on the initial mean field energy and size of the condensate. We
compare experimental results with simulations of the Gross-Pitaevski equation.
A comparison with the behaviour of bouncing thermal clouds allows to identify
quantum features specific for condensates.Comment: 4 page
An adaptive inelastic magnetic mirror for Bose-Einstein condensates
We report the reflection and focussing of a Bose-Einstein condensate by a new
pulsed magnetic mirror. The mirror is adaptive, inelastic, and of extremely
high optical quality. The deviations from specularity are less than 0.5 mrad
rms, making this the best atomic mirror demonstrated to date. We have also used
the mirror to realize the analog of a beam-expander, producing an ultra-cold
collimated fountain of matter wavesComment: 4 pages, 4 figure
Quantum damping of position due to energy measurements
Quantum theory for measurements of energy is introduced and its consequences
for the average position of monitored dynamical systems are analyzed. It turns
out that energy measurements lead to a localization of the expectation values
of other observables. This is manifested, in the case of position, as a damping
of the motion without classical analogue. Quantum damping of position for an
atom bouncing on a reflecting surface in presence of a homogeneous
gravitational field is dealt in detail and the connection with an experiment
already performed in the classical regime is studied. We show that quantum
damping is testable provided that the same measurement strength obtained in the
experimental verification of the quantum Zeno effect in atomic spectroscopy [W.
M. Itano et al., Phys. Rev. A {\bf 41}, 2295 (1990)] is made available.Comment: 19 pages + 4 figures available upon request; Plain REVTeX; To be
published in Phys. Rev.
Fractional quantum revivals in the atomic gravitational cavity
In this paper we discuss the quantum dynamics and fractional quantum revivals of an integrable nonlinear system, consisting of an atom bouncing vertically from an evanescent field, for two cases with the simplified infinite-potential and the more practical exponential potential, respectively. We study the two cases separately, then contrast and compare the results and reach the conclusion that provided the starting position of the atoms is not too close to the reflecting surface supporting the evanescent wave (this condition is always satisfied in present experiments in this field), the two cases will produce the same results. This means that the idealized infinite potential is a good approximation to the more realistic exponential potential. Because the quantum analysis of the infinite-potential case is quite simple and straighforward (since its Schrödinger equation has analytical solutions), this will greatly simplify the quantum analysis of the more complicated exponential potential case and hence has practical significance
Quantum Revivals in Periodically Driven Systems close to nonlinear resonance
We calculate the quantum revival time for a wave-packet initially well
localized in a one-dimensional potential in the presence of an external
periodic modulating field. The dependence of the revival time on various
parameters of the driven system is shown analytically. As an example of
application of our approach, we compare the analytically obtained values of the
revival time for various modulation strengths with the numerically computed
ones in the case of a driven gravitational cavity. We show that they are in
very good agreement.Comment: 14 pages, 1 figur
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