341 research outputs found
Theory of dark resonances for alkali vapors in a buffer-gas cell
We develop an analytical theory of dark resonances that accounts for the full
atomic-level structure, as well as all field-induced effects such as coherence
preparation, optical pumping, ac Stark shifts, and power broadening. The
analysis uses a model based on relaxation constants that assumes the total
collisional depolarization of the excited state. A good qualitative agreement
with experiments for Cs in Ne is obtained.Comment: 16 pages; 7 figures; revtex4. Accepted for publication in PR
Cancellation of light-shifts in an N-resonance clock
We demonstrate that first-order light-shifts can be cancelled for an
all-optical, three-photon-absorption resonance ("N-resonance") on the D1
transition of Rb87. This light-shift cancellation enables improved frequency
stability for an N-resonance clock. For example, using a table-top apparatus
designed for N-resonance spectroscopy, we measured a short-term fractional
frequency stability (Allan deviation) 1.5e-11 tau^(-1/2) for observation times
1s< tau < 50s. Further improvements in frequency stability should be possible
with an apparatus designed as a dedicated N-resonance clock.Comment: 4 pages, 4 figure
Comparison of 87Rb N-resonances for D1 and D2 transitions
We report an experimental comparison of three-photon-absorption resonances
(known as "N-resonances") for the D_1 and D_2 optical transitions of thermal
87Rb vapor. We find that the D_2 N-resonance has better contrast, a broader
linewidth, and a more symmetric lineshape than the D_1 N-resonance. Taken
together, these factors imply superior performance for frequency standards
operating on alkali D_2 N-resonances, in contrast to coherent population
trapping (CPT) resonances for which the D_2 transition provides poorer
frequency standard performance than the D_1 transition.Comment: 3 pages, 4 figure
Absorption resonance and large negative delay in Rb vapor with buffer gas
We observe a narrow, isolated, two-photon absorption resonance in Rb for
large one-photon detuning in the presence of a buffer gas. In the absence of
buffer gas, a standard Lambda configuration of two laser frequencies gives rise
to electromagnetically induced transparency (EIT) for all values of one-photon
detuning throughout the inhomogeneously (Doppler) broadened line. However, when
a buffer gas is added and the one-photon detuning is comparable to or greater
than the Doppler width, an absorption resonance appears instead of the usual
EIT resonance. We also observe large negative group delay (~ -300 us for a
Gaussian pulse propagating through the media with respect to a reference pulse
not affected by the media), corresponding to a superluminal group velocity v_g=
-c/(3.6x10^6)=-84 m/s.Comment: 4 pages, 5 figure
Cold atoms in videotape micro-traps
We describe an array of microscopic atom traps formed by a pattern of
magnetisation on a piece of videotape. We describe the way in which cold atoms
are loaded into one of these micro-traps and how the trapped atom cloud is used
to explore the properties of the trap. Evaporative cooling in the micro-trap
down to a temperature of 1 microkelvin allows us to probe the smoothness of the
trapping potential and reveals some inhomogeneity produced by the magnetic
film. We discuss future prospects for atom chips based on microscopic
permanent-magnet structures.Comment: Submitted for EPJD topical issue "Atom chips: manipulating atoms and
molecules with microfabricated structures
A surface-patterned chip as a strong source of ultracold atoms for quantum technologies
Laser-cooled atoms are central to modern precision measurements. They are also increasingly important as an enabling technology for experimental cavity quantum electrodynamics, quantum information processing and matterâwave interferometry. Although significant progress has been made in miniaturizing atomic metrological devices, these are limited in accuracy by their use of hot atomic ensembles and buffer gases. Advances have also been made in producing portable apparatus that benefits from the advantages of atoms in the microkelvin regime. However, simplifying atomic cooling and loading using microfabrication technology has proved difficult. In this Letter we address this problem, realizing an atom chip that enables the integration of laser cooling and trapping into a compact apparatus. Our source delivers ten thousand times more atoms than previous magneto-optical traps with microfabricated optics and, for the first time, can reach sub-Doppler temperatures. Moreover, the same chip design offers a simple way to form stable optical lattices. These features, combined with simplicity of fabrication and ease of operation, make these new traps a key advance in the development of cold-atom technology for high-accuracy, portable measurement devices
An Improved Neutron Electric Dipole Moment Experiment
A new measurement of the neutron EDM, using Ramsey's method of separated
oscillatory fields, is in preparation at the new high intensity source of
ultra-cold neutrons (UCN) at the Paul Scherrer Institute, Villigen, Switzerland
(PSI). The existence of a non-zero nEDM would violate both parity and time
reversal symmetry and, given the CPT theorem, might lead to a discovery of new
CP violating mechanisms. Already the current upper limit for the nEDM
(|d_n|<2.9E-26 e.cm) constrains some extensions of the Standard Model.
The new experiment aims at a two orders of magnitude reduction of the
experimental uncertainty, to be achieved mainly by (1) the higher UCN flux
provided by the new PSI source, (2) better magnetic field control with improved
magnetometry and (3) a double chamber configuration with opposite electric
field directions.
The first stage of the experiment will use an upgrade of the RAL/Sussex/ILL
group's apparatus (which has produced the current best result) moved from
Institut Laue-Langevin to PSI. The final accuracy will be achieved in a further
step with a new spectrometer, presently in the design phase.Comment: Flavor Physics & CP Violation Conference, Taipei, 200
Evanescent light-matter Interactions in Atomic Cladding Wave Guides
Alkali vapors, and in particular rubidium, are being used extensively in
several important fields of research such as slow and stored light non-linear
optics3 and quantum computation. Additionally, the technology of alkali vapors
plays a major role in realizing myriad industrial applications including for
example atomic clocks magentometers8 and optical frequency stabilization.
Lately, there is a growing effort towards miniaturizing traditional
centimeter-size alkali vapor cells. Owing to the significant reduction in
device dimensions, light matter interactions are greatly enhanced, enabling new
functionalities due to the low power threshold needed for non-linear
interactions. Here, taking advantage of the mature Complimentary
Metal-Oxide-Semiconductor (CMOS) compatible platform of silicon photonics, we
construct an efficient and flexible platform for tailored light vapor
interactions on a chip. Specifically, we demonstrate light matter interactions
in an atomic cladding wave guide (ACWG), consisting of CMOS compatible silicon
nitride nano wave-guide core with a Rubidium (Rb) vapor cladding. We observe
the highly efficient interaction of the electromagnetic guided mode with the
thermal Rb cladding. The nature of such interactions is explained by a model
which predicts the transmission spectrum of the system taking into account
Doppler and transit time broadening. We show, that due to the high confinement
of the optical mode (with a mode area of 0.3{\lambda}2), the Rb absorption
saturates at powers in the nW regime.Comment: 10 Pages 4 Figures. 1 Supplementar
Effects of urodilatin on natriuresis in cirrhosis patients with sodium retention
BACKGROUND: Sodium retention and ascites are serious clinical problems in cirrhosis. Urodilatin (URO) is a peptide with paracrine effects in decreasing sodium reabsorption in the distal nephron. Our aim was to investigate the renal potency of synthetic URO on urine sodium excretion in cirrhosis patients with sodium retention and ascites. METHODS: Seven cirrhosis patients with diuretics-resistant sodium retention received a short-term (90 min) infusion of URO in a single-blind, placebo-controlled cross-over study. In the basal state after rehydration the patients had urine sodium excretion < 50 mmol/24 h. RESULTS: URO transiently increased urine sodium excretion from 22 ± 16 Όmol/min (mean ± SD) to 78 ± 41 Όmol/min (P < 0.05) and there was no effect of placebo (29 ± 14 to 44 ± 32). The increase of URO's second messenger after the receptor, cGMP, was normal. URO had no effect on urine flow or on blood pressure. Most of the patients had highly elevated plasma levels of renin, angiotensin II and aldosterone and URO did not change these. CONCLUSION: The short-term low-dose URO infusion increased the sodium excretion of the patients. The increase was small but systematic and potentially clinically important for such patients. The small response contrasts the preserved responsiveness of the URO receptors. The markedly activated systemic pressor hormones in cirrhosis evidently antagonized the local tubular effects of URO
5-Thia-5-Deazaflavin, a 1e â -Transferring Flavin Analog
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65939/1/j.1432-1033.1979.tb12952.x.pd
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