675 research outputs found
Influence of modulation frequency in rubidium cell frequency standards
The error signal which is used to control the frequency of the quartz crystal oscillator of a passive rubidium cell frequency standard is considered. The value of the slope of this signal, for an interrogation frequency close to the atomic transition frequency is calculated and measured for various phase (or frequency) modulation waveforms, and for several values of the modulation frequency. A theoretical analysis is made using a model which applies to a system in which the optical pumping rate, the relaxation rates and the RF field are homogeneous. Results are given for sine-wave phase modulation, square-wave frequency modulation and square-wave phase modulation. The influence of the modulation frequency on the slope of the error signal is specified. It is shown that the modulation frequency can be chosen as large as twice the non-saturated full-width at half-maximum without a drastic loss of the sensitivity to an offset of the interrogation frequency from center line, provided that the power saturation factor and the amplitude of modulation are properly adjusted
Cold Atom Clock Test of Lorentz Invariance in the Matter Sector
We report on a new experiment that tests for a violation of Lorentz
invariance (LI), by searching for a dependence of atomic transition frequencies
on the orientation of the spin of the involved states (Hughes-Drever type
experiment). The atomic frequencies are measured using a laser cooled
Cs atomic fountain clock, operating on a particular combination of
Zeeman substates. We analyze the results within the framework of the Lorentz
violating standard model extension (SME), where our experiment is sensitive to
a largely unexplored region of the SME parameter space, corresponding to first
measurements of four proton parameters and improvements by 11 and 13 orders of
magnitude on the determination of four others. In spite of the attained
uncertainties, and of having extended the search into a new region of the SME,
we still find no indication of LI violation.Comment: 4 pages, accepted for Physical Review Letter
Peregrine falcon survival rates derived from a long-term study at a migratory and overwintering area in coastal Washington
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CIVET a Controlled Intrusiveness Verification Technology
CIVET is a proposed concept for Arms Control verification capable of using information while preserving its confidentiality, in a bilateral environment
Laser frequency stabilization to a single ion
A fundamental limit to the stability of a single-ion optical frequency
standard is set by quantum noise in the measurement of the internal state of
the ion. We discuss how the interrogation sequence and the processing of the
atomic resonance signal can be optimized in order to obtain the highest
possible stability under realistic experimental conditions. A servo algorithm
is presented that stabilizes a laser frequency to the single-ion signal and
that eliminates errors due to laser frequency drift. Numerical simulations of
the servo characteristics are compared to experimental data from a frequency
comparison of two single-ion standards based on a transition at 688 THz in
171Yb+. Experimentally, an instability sigma_y(100 s)=9*10^{-16} is obtained in
the frequency difference between both standards.Comment: 15 pages, 5 figures, submitted to J. Phys.
Reverse genetics in Candida albicans predicts ARF cycling is essential for drug resistance and virulence
Peer reviewedPublisher PD
Collisional shifts in optical-lattice atom clocks
We theoretically study the effects of elastic collisions on the determination
of frequency standards via Ramsey fringe spectroscopy in optical-lattice atom
clocks. Interparticle interactions of bosonic atoms in multiply-occupied
lattice sites can cause a linear frequency shift, as well as generate
asymmetric Ramsey fringe patterns and reduce fringe visibility due to
interparticle entanglement. We propose a method of reducing these collisional
effects in an optical lattice by introducing a phase difference of
between the Ramsey driving fields in adjacent sites. This configuration
suppresses site to site hopping due to interference of two tunneling pathways,
without degrading fringe visibility. Consequently, the probability of double
occupancy is reduced, leading to cancellation of collisional shifts.Comment: 15 pages, 11 figure
Precise determination of Li cold collision parameters by radio-frequency spectroscopy on weakly bound molecules
We employ radio-frequency spectroscopy on weakly bound Li molecules
to precisely determine the molecular binding energies and the energy splittings
between molecular states for different magnetic fields. These measurements
allow us to extract the interaction parameters of ultracold Li atoms based
on a multi-channel quantum scattering model. We determine the singlet and
triplet scattering lengths to be and (1
= 0.0529177 nm), and the positions of the broad Feshbach resonances in
the energetically lowest three wave scattering channels to be 83.41(15) mT,
69.04(5) mT, and 81.12(10) mT
Services and Staffing Practices within Academic Libraries Serving College of Osteopathic Medicine Programs: A Mixed Methods Study
This study provides a systematic comparison of services and staffing within academic health sciences libraries serving College of Osteopathic Medicine programs in the U.S. Library directors, not only those affiliated with new medical schools, but also with long- standing, and more traditional schools, can use this data to make a case for new resources, services, or staffing. In addition, medical school administrators may find opportunities in this study’s results for more productive collaborations with the library, in areas such as curriculum-integrated instruction, research development, and scholarly publishing. Finally, leaders within developing medical schools will become better informed about current library services being provided, and staffing trends, in order to plan for an appropriate budget and staffing for their future health sciences libraries
Mean field ground state of a spin-1 condensate in a magnetic field
We revisit the topic of the mean field ground state of a spin-1 atomic
condensate inside a uniform magnetic field () under the constraints that
both the total number of atoms () and the magnetization () are
conserved. In the presence of an internal state (spin component) independent
trap, we also investigate the dependence of the so-called single spatial mode
approximation (SMA) on the magnitude of the magnetic field and . Our
result indicate that the quadratic Zeeman effect is an important factor in
balancing the mean field energy from elastic atom-atom collisions that are
known to conserve both and .Comment: 13 pages, 9 figures, to be published in New J. Phys.
(http://www.njp.org/
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