84 research outputs found
Magnetic blackbody shift of hyperfine transitions for atomic clocks
We derive an expression for the magnetic blackbody shift of hyperfine
transitions such as the cesium primary reference transition which defines the
second. The shift is found to be a complicated function of temperature, and has
a T^2 dependence only in the high-temperature limit. We also calculate the
shift of ground-state p_1/2 hyperfine transitions which have been proposed as
new atomic clock transitions. In this case interaction with the p_3/2
fine-structure multiplet may be the dominant effect
Solid State Systems for Electron Electric Dipole Moment and other Fundamental Measurements
In 1968, F.L. Shapiro published the suggestion that one could search for an
electron EDM by applying a strong electric field to a substance that has an
unpaired electron spin; at low temperature, the EDM interaction would lead to a
net sample magnetization that can be detected with a SQUID magnetometer. One
experimental EDM search based on this technique was published, and for a number
of reasons including high sample conductivity, high operating temperature, and
limited SQUID technology, the result was not particularly sensitive compared to
other experiments in the late 1970's.
Advances in SQUID and conventional magnetometery had led us to reconsider
this type of experiment, which can be extended to searches and tests other than
EDMs (e.g., test of Lorentz invariance). In addition, the complementary
measurement of an EDM-induced sample electric polarization due to application
of a magnetic field to a paramagnetic sample might be effective using modern
ultrasensitive charge measurement techniques. A possible paramagnetic material
is Gd-substituted YIG which has very low conductivity and a net enhancement
(atomic enhancement times crystal screening) of order unity. Use of a
reasonable volume (100's of cc) sample of this material at 50 mK and 10 kV/cm
might yield an electron EDM sensitivity of e cm or better, a factor
of improvement over current experimental limits.Comment: 6 pages. Prepared for ITAMP workshop on fundamental physics that was
to be held Sept 20-22 2001 in Cambride, MA, but was canceled due to terrorist
attack on U.S New version incorporates a number of small changes, most
notably the scaling of the sensitivity of the Faraday magnetometer with
linewidth is now treated in a saner fashion. The possibility of operating at
an even lower temperarture, say 10 microkelvin, is also discusse
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
Colloquium: Comparison of Astrophysical and Terrestrial Frequency Standards
We have re-analyzed the stability of pulse arrival times from pulsars and
white dwarfs using several analysis tools for measuring the noise
characteristics of sampled time and frequency data. We show that the best
terrestrial artificial clocks substantially exceed the performance of
astronomical sources as time-keepers in terms of accuracy (as defined by cesium
primary frequency standards) and stability. This superiority in stability can
be directly demonstrated over time periods up to two years, where there is high
quality data for both. Beyond 2 years there is a deficiency of data for
clock/clock comparisons and both terrestrial and astronomical clocks show equal
performance being equally limited by the quality of the reference timescales
used to make the comparisons. Nonetheless, we show that detailed accuracy
evaluations of modern terrestrial clocks imply that these new clocks are likely
to have a stability better than any astronomical source up to comparison times
of at least hundreds of years. This article is intended to provide a correct
appreciation of the relative merits of natural and artificial clocks. The use
of natural clocks as tests of physics under the most extreme conditions is
entirely appropriate; however, the contention that these natural clocks,
particularly white dwarfs, can compete as timekeepers against devices
constructed by mankind is shown to be doubtful.Comment: 9 pages, 2 figures; presented at the International Frequency Control
Symposium, Newport Beach, Calif., June, 2010; presented at Pulsar Conference
2010, October 12th, Sardinia; accepted 13th September 2010 for publication in
Reviews of Modern Physic
First Accuracy Evaluation of NIST-F2
We report the first accuracy evaluation of NIST-F2, a second-generation laser-cooled Cesium fountain primary standard developed at the National Institute of Standards and Technology (NIST) with a cryogenic (Liquid Nitrogen) microwave cavity and flight region. The 80 K atom interrogation environment reduces the uncertainty due to the Blackbody Radiation (BBR) shift by more than a factor of 50. Also, the Ramsey microwave cavity exhibits a high Q (>50,000) at this low temperature, resulting in a reduced distributed cavity phase shift. NIST-F2 has undergone many tests and improvements since we first began operation in 2008. In the last few years NIST-F2 has been compared against a NIST maser time scale and NIST-F1 (the US primary frequency standard) as part of in-house accuracy evaluations. We report the results of nine in-house comparisons since 2010 with a focus on the most recent accuracy evaluation. This paper discusses the design of the physics package, the laser and optics systems, and the accuracy evaluation methods. The Type B fractional uncertainty of NIST-F2 is shown to be 0.11 × 10-15 and is dominated by microwave amplitude dependent effects. The most recent evaluation (August 2013) had a statistical (Type A) fractional uncertainty of 0.44 × 10-15
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
Efficient Photoionization-Loading of Trapped Cadmium Ions with Ultrafast Pulses
Atomic cadmium ions are loaded into radiofrequency ion traps by
photoionization of atoms in a cadmium vapor with ultrafast laser pulses. The
photoionization is driven through an intermediate atomic resonance with a
frequency-quadrupled mode-locked Ti:Sapphire laser that produces pulses of
either 100 fsec or 1 psec duration at a central wavelength of 229 nm. The large
bandwidth of the pulses photoionizes all velocity classes of the Cd vapor,
resulting in high loading efficiencies compared to previous ion trap loading
techniques. Measured loading rates are compared with a simple theoretical
model, and we conclude that this technique can potentially ionize every atom
traversing the laser beam within the trapping volume. This may allow the
operation of ion traps with lower levels of background pressures and less trap
electrode surface contamination. The technique and laser system reported here
should be applicable to loading most laser-cooled ion species.Comment: 11 pages, 12 figure
Cooling the Collective Motion of Trapped Ions to Initialize a Quantum Register
We report preparation in the ground state of collective modes of motion of
two trapped 9Be+ ions. This is a crucial step towards realizing quantum logic
gates which can entangle the ions' internal electronic states. We find that
heating of the modes of relative ion motion is substantially suppressed
relative to that of the center-of-mass modes, suggesting the importance of
these modes in future experiments.Comment: 5 pages, including 3 figures. RevTeX. PDF and PostScript available at
http://www.bldrdoc.gov/timefreq/ion/qucomp/papers.htm . final (published)
version. Eq. 1 and Table 1 slightly different from original submissio
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