890 research outputs found
Dissolved iron in the tropical and subtropical Atlantic Ocean
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95150/1/gbc1254.pd
Sub-dekahertz ultraviolet spectroscopy of 199Hg+
Using a laser that is frequency-locked to a Fabry-Perot etalon of high
finesse and stability, we probe the 5d10 6s 2S_1/2 (F=0) - 5d9 6s 2D_5/2 (F=2)
Delta-m_F = 0 electric-quadrupole transition of a single laser-cooled 199Hg+
ion stored in a cryogenic radio-frequency ion trap. We observe
Fourier-transform limited linewidths as narrow as 6.7 Hz at 282 nm (1.06 X
10^15 Hz), yielding a line Q = 1.6 X 10^14. We perform a preliminary
measurement of the 5d9 6s2 2D_5/2 electric-quadrupole shift due to interaction
with the static fields of the trap, and discuss the implications for future
trapped-ion optical frequency standards.Comment: 4 pages, 4 figures, submitted for publicatio
Tunneling Ionization Rates from Arbitrary Potential Wells
We present a practical numerical technique for calculating tunneling
ionization rates from arbitrary 1-D potential wells in the presence of a linear
external potential by determining the widths of the resonances in the spectral
density, rho(E), adiabatically connected to the field-free bound states. While
this technique applies to more general external potentials, we focus on the
ionization of electrons from atoms and molecules by DC electric fields, as this
has an important and immediate impact on the understanding of the multiphoton
ionization of molecules in strong laser fields.Comment: 13 pages, 7 figures, LaTe
Quantum state manipulation of trapped atomic ions
A single laser-cooled and trapped 9Be+ ion is used to investigate methods of
coherent quantum-state synthesis and quantum logic. We create and characterize
nonclassical states of motion including "Schroedinger-cat" states. A
fundamental quantum logic gate is realized which uses two states of the
quantized ion motion and two ion internal states as qubits. We explore some of
the applications for, and problems in realizing, quantum computation based on
multiple trapped ions.Comment: Postscript only. 21 pages text, 5 figures., Proc. Workshop on Quantum
Computing, Santa Barbara, CA, Dec. 1996, Submitted to Proc. Roy. Soc.
Testing the stability of fundamental constants with the 199Hg+ single-ion optical clock
Over a two-year duration, we have compared the frequency of the 199Hg+ 5d106s
2S 1/2 (F=0) 5d9 6s2 2D 5/2 (F=2) electric-quadrupole transition at 282 nm
with the frequency of the ground-state hyperfine splitting in neutral 133Cs.
These measurements show that any fractional time variation of the ratio
nu(Cs)/nu(Hg) between the two frequencies is smaller than +/- 7 10^-15 / yr (1
sigma uncertainty). According to recent atomic structure calculations, this
sets an upper limit to a possible fractional time variation of g(Cs) m_e / m_p
alpha^6.0 at the same level.Comment: 4 pages with 3 figures. RevTeX 4, Submitted to Phys. Rev. Let
Absolute Frequency Measurements of the Hg^+ and Ca Optical Clock Transitions with a Femtosecond Laser
The frequency comb created by a femtosecond mode-locked laser and a
microstructured fiber is used to phase coherently measure the frequencies of
both the Hg^+ and Ca optical standards with respect to the SI second as
realized at NIST. We find the transition frequencies to be f_Hg=1 064 721 609
899 143(10) Hz and f_Ca=455 986 240 494 158(26) Hz, respectively. In addition
to the unprecedented precision demonstrated here, this work is the precursor to
all-optical atomic clocks based on the Hg^+ and Ca standards. Furthermore, when
combined with previous measurements, we find no time variations of these atomic
frequencies within the uncertainties of |(df_Ca/dt)/f_Ca| < 8 x 10^{-14}
yr^{-1}, and |(df_Hg/dt)/f_Hg|< 30 x 10^{-14} yr^{-1}.Comment: 6 pages, including 4 figures. RevTex 4. Submitted to Phys. Rev. Let
A New Option for a Search for Alpha Variation: Narrow Transitions with Enhanced Sensitivity
We consider several transitions between narrow lines that have an enhanced
sensitivity to a possible variation of the fine structure constant, alpha. This
enhancement may allow a search to be performed with an effective suppression of
the systematic sources of uncertainty that are unavoidable in conventional
high-resolution spectroscopic measurements. In the future this may provide the
strongest laboratory constraints on alpha variation
Quantum control, quantum information processing, and quantum-limited metrology with trapped ions
We briefly discuss recent experiments on quantum information processing using
trapped ions at NIST. A central theme of this work has been to increase our
capabilities in terms of quantum computing protocols, but we have also applied
the same concepts to improved metrology, particularly in the area of frequency
standards and atomic clocks. Such work may eventually shed light on more
fundamental issues, such as the quantum measurement problem.Comment: Proceedings of the International Conference on Laser Spectroscopy
(ICOLS), 10 pages, 5 figure
Some Like It Fat: Comparative Ultrastructure of the Embryo in Two Demosponges of the Genus Mycale (Order Poecilosclerida) from Antarctica and the Caribbean
0000-0002-7993-1523© 2015 Riesgo et al. This is an open access article distributed under the terms of the Creative Commons Attribution License [4.0], which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article
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