847 research outputs found
Cold Atomic Collisions: Coherent Control of Penning and Associative Ionization
Coherent Control techniques are computationally applied to cold (1mK < T < 1
K) and ultracold (T < 1 microK) Ne*(3s,3P2) + Ar(1S0) collisions. We show that
by using various initial superpositions of the Ne*(3s,3P2) M = {-2,-1,0,1,2}
Zeeman sub-levels it is possible to reduce the Penning Ionization (PI) and
Associative Ionization (AI) cross sections by as much as four orders of
magnitude. It is also possible to drastically change the ratio of these two
processes. The results are based on combining, within the "Rotating Atom
Approximation", empirical and ab-initio ionization-widths.Comment: 4 pages, 2 tables, 2 figure
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
Test of Lorentz Symmetry by using a 3He/129Xe Co-Magnetometer
To test Lorentz symmetry we used a 3He/129Xe co-magnetometer. We will give a
short summary of our experimental setup and the results of our latest
measurements. We obtained preliminary results for the equatorial component of
the background field interacting with the spin of the bound neutron: b_n < 3.72
x 10^(-32) GeV (95 C.L.).Comment: Presented at the Fifth Meeting on CPT and Lorentz Symmetry,
Bloomington, Indiana, June 28 - July 2, 201
Correcting heading errors in optically pumped magnetometers through microwave interrogation
We demonstrate how to measure in-situ for heading errors of optically pumped
magnetometers in geomagnetic fields. For this, we implement microwave-driven
Rabi oscillations and Ramsey interferometry on hyperfine transitions as two
independent methods to detect scalar systematics of free induction decay (FID)
signals. We showcase the wide applicability of this technique by operating in
the challenging parameter regime of compact vapor cells with imperfect pumping
and high buffer gas pressure. In this system, we achieve suppression of large
inaccuracies arising from nonlinear Zeeman (NLZ) shifts by up to a factor of 10
to levels below 0.6 nT. In the Ramsey method we accomplish this, even in
arbitrary magnetic field directions, by employing a hyper-Ramsey protocol and
optical pumping with adiabatic power ramps. For the Rabi technique, this level
of accuracy is reached, despite associated drive-dependent shifts, by
referencing Rabi frequency measurements to a complete atom-microwave coupling
model that incorporates the microwave polarization structure.Comment: 6 pages, 4 figures + supplementary 16 pages, 10 figure
The hyperfine Paschen-Back Faraday effect
We investigate experimentally and theoretically the Faraday effect in an atomic medium in the hyperfine Paschen–Back regime, where the Zeeman interaction is larger than the hyperfine splitting. We use a small permanent magnet and a micro-fabricated vapour cell, giving magnetic fields of the order of a tesla. We show that for low absorption and small rotation angles, the refractive index is well approximated by the Faraday rotation signal, giving a simple way to measure the atomic refractive index. Fitting to the atomic spectra, we achieve magnetic field sensitivity at the 10−4 level. Finally we note that the Faraday signal shows zero crossings which can be used as temperature insensitive error signals for laser frequency stabilization at large detuning. The theoretical sensitivity for 87Rb is found to be ~40 kHz °C−1
Topoisomer Differentiation of Molecular Knots by FTICR MS: Lessons from Class II Lasso Peptides
Lasso peptides constitute a class of bioactive peptides sharing a knotted
structure where the C-terminal tail of the peptide is threaded through and
trapped within an N-terminalmacrolactamring. The structural characterization of
lasso structures and differentiation from their unthreaded topoisomers is not
trivial and generally requires the use of complementary biochemical and
spectroscopic methods. Here we investigated two antimicrobial peptides
belonging to the class II lasso peptide family and their corresponding
unthreaded topoisomers: microcin J25 (MccJ25), which is known to yield
two-peptide product ions specific of the lasso structure under collisioninduced
dissociation (CID), and capistruin, for which CID does not permit to
unambiguously assign the lasso structure. The two pairs of topoisomers were
analyzed by electrospray ionization Fourier transform ion cyclotron resonance
mass spectrometry (ESI-FTICR MS) upon CID, infrared multiple photon
dissociation (IRMPD), and electron capture dissociation (ECD). CID and
ECDspectra clearly permitted to differentiate MccJ25 from its non-lasso
topoisomer MccJ25-Icm, while for capistruin, only ECD was informative and
showed different extent of hydrogen migration (formation of c\bullet/z from
c/z\bullet) for the threaded and unthreaded topoisomers. The ECD spectra of the
triply-charged MccJ25 and MccJ25-lcm showed a series of radical b-type product
ions {\eth}b0In{\TH}. We proposed that these ions are specific of
cyclic-branched peptides and result from a dual c/z\bullet and y/b
dissociation, in the ring and in the tail, respectively. This work shows the
potentiality of ECD for structural characterization of peptide topoisomers, as
well as the effect of conformation on hydrogen migration subsequent to electron
capture
Die Viehwirtschaft im Gebiet Kaliningrad: zum Transformationsprozeß im ländlichen Raum
The livestock economy played an important role in the agriculture of the area around Kaliningrad until the end of the eighties. Particularly the milk economy, but also the breeding of beef and pork were significant sources of income for the large agricultural firms. The changes in the economic situation of the agricultural firms went hand in hand with the changes in the economic and political situation. The privatisation of the old combines primarily lead to them taking on a new legal form. All other changes and transformations took longer to assert themselves. New, private agricultural firms were also founded, however, these are equipped with a small amount of land and, above all, very little capital resources. This shortage of finances which affects all companies, regardless of their legal forms, has considerable effects on the lives tock industry. The livestock figures which, during the period of the socialist planned economy, were distributed relatively evenly across the entire area, are dropping and are concentrated on certain favourable areas. The newly created private firms generally have low numbers of cattle, due to the fact that they are unable to invest in barns, breeding animals and high performance fodder. Should the urgently required measures for the support of the animal production fail to be im plemented by the regional administration over a long period of time, then the fear would be justified that the agriculture will suffer a setback which it will hardly be able to compensate. The continued exodus of young and well educated specialists from the agricultural sector will continue further and the percentage of old people in the village population will increase. To a growing extent, a subsistence economy is being operated which will further hinder the competitiveness of the agriculture in the region around Kaliningrad in comparison to, e.g. the neighbouring states of Poland and Lithuania
Limit on Lorentz and CPT violation of the bound Neutron Using a Free Precession 3He/129Xe co-magnetometer
We report on the search for Lorentz violating sidereal variations of the
frequency difference of co-located spin-species while the Earth and hence the
laboratory reference frame rotates with respect to a relic background field.
The co-magnetometer used is based on the detection of freely precessing nuclear
spins from polarized 3He and 129Xe gas samples using SQUIDs as low-noise
magnetic flux detectors. As result we can determine the limit for the
equatorial component of the background field interacting with the spin of the
bound neutron to be bn < 3.7 x 10^{-32} GeV (95 C.L.).Comment: 5 pages, 4 figure
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