623 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
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
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
Transitional Care for Patients with Congenital Colorectal Diseases : An EUPSA Network Office, ERNICA, and eUROGEN Joint Venture
Publisher Copyright: © 2023 The Author(s)BACKGROUND: Transition of care (TOC; from childhood into adulthood) of patients with anorectal malformations (ARM) and Hirschsprung disease (HD) ensures continuation of care for these patients. The aim of this international study was to assess the current status of TOC and adult care (AC) programs for patients with ARM and HD. METHODS: A survey was developed by members of EUPSA, ERN eUROGEN, and ERNICA, including patient representatives (ePAGs), comprising of four domains: general information, general questions about transition to adulthood, and disease-specific questions regarding TOC and AC programs. Recruitment of centres was done by the ERNs and EUPSA, using mailing lists and social media accounts. Only descriptive statistics were reported. RESULTS: In total, 82 centres from 21 different countries entered the survey. Approximately half of them were ERN network members. Seventy-two centres (87.8%) had a self-reported area of expertise for both ARM and HD. Specific TOC programs were installed in 44% of the centres and AC programs in 31% of these centres. When comparing centres, wide variation was observed in the content of the programs. CONCLUSION: Despite the awareness of the importance of TOC and AC programs, these programs were installed in less than 50% of the participating centres. Various transition and AC programs were applied, with considerable heterogeneity in implementation, content and responsible caregivers involved. Sharing best practice examples and taking into account local and National Health Care Programs might lead to a better continuation of care in the future. LEVEL OF EVIDENCE: III.Peer reviewe
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
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.
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
Optics with an Atom Laser Beam
We report on the atom optical manipulation of an atom laser beam. Reflection,
focusing and its storage in a resonator are demonstrated. Precise and versatile
mechanical control over an atom laser beam propagating in an inhomogeneous
magnetic field is achieved by optically inducing spin-flips between atomic
ground states with different magnetic moment. The magnetic force acting on the
atoms can thereby be effectively switched on and off. The surface of the atom
optical element is determined by the resonance condition for the spin-flip in
the inhomogeneous magnetic field. A mirror reflectivity of more than 98% is
measured
Creating a low-dimensional quantum gas using dark states in an inelastic evanescent-wave mirror
We discuss an experimental scheme to create a low-dimensional gas of
ultracold atoms, based on inelastic bouncing on an evanescent-wave mirror.
Close to the turning point of the mirror, the atoms are transferred into an
optical dipole trap. This scheme can compress the phase-space density and can
ultimately yield an optically-driven atom laser. An important issue is the
suppression of photon scattering due to ``cross-talk'' between the mirror
potential and the trapping potential. We propose that for alkali atoms the
photon scattering rate can be suppressed by several orders of magnitude if the
atoms are decoupled from the evanescent-wave light. We discuss how such dark
states can be achieved by making use of circularly-polarized evanescent waves.Comment: 8 pages, 4 figure
The Fermi accelerator in atom optics
We study the classical and quantum dynamics of a Fermi accelerator realized
by an atom bouncing off a modulated atomic mirror. We find that in a window of
the modulation amplitude dynamical localization occurs in both position and
momentum. A recent experiment [A. Steane, P. Szriftgiser, P. Desbiolles, and J.
Dalibard, Phys. Rev. Lett. {\bf 74}, 4972 (1995)] shows that this system can be
implemented experimentally.Comment: 5 pages, 5 figure
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