133 research outputs found
Frequency comparisons and absolute frequency measurements of 171Yb+ single-ion optical frequency standards
We describe experiments with an optical frequency standard based on a laser
cooled Yb ion confined in a radiofrequency Paul trap. The
electric-quadrupole transition from the ground state to the
state at the wavelength of 436 nm is used as the reference
transition. In order to compare two Yb standards, separate
frequency servo systems are employed to stabilize two probe laser frequencies
to the reference transition line centers of two independently stored ions. The
experimental results indicate a relative instability (Allan standard deviation)
of the optical frequency difference between the two systems of only, so that shifts in the sub-hertz range can be
resolved. Shifts of several hertz are observed if a stationary electric field
gradient is superimposed on the radiofrequency trap field. The absolute optical
transition frequency of Yb at 688 THz was measured with a cesium atomic
clock at two times separated by 2.8 years. A temporal variation of this
frequency can be excluded within a relative uncertainty of yr. Combined with recently published values for the constancy
of other transition frequencies this measurement provides a limit on the
present variability of the fine structure constant at the level of
yr.Comment: 12 pages, 5 figures, Proceedings of MPLP'04, Novosibirsk, August
22.-27., 200
High-accuracy optical clock based on the octupole transition in 171Yb+
We experimentally investigate an optical frequency standard based on the 467
nm (642 THz) electric-octupole reference transition 2S1/2(F=0) -> F7/2(F=3) in
a single trapped 171Yb+ ion. The extraordinary features of this transition
result from the long natural lifetime and from the 4f136s2 configuration of the
upper state. The electric quadrupole moment of the 2F7/2 state is measured as
-0.041(5) e(a0)^2, where e is the elementary charge and a0 the Bohr radius. We
also obtain information on the differential scalar and tensorial components of
the static polarizability and of the probe light induced ac Stark shift of the
octupole transition. With a real-time extrapolation scheme that eliminates this
shift, the unperturbed transition frequency is realized with a fractional
uncertainty of 7.1x10^(-17). The frequency is measured as 642 121 496 772
645.15(52) Hz.Comment: 5 pages, 4 figure
A generalized Ramsey excitation scheme with suppressed light shift
We experimentally investigate a recently proposed optical excitation scheme
[V.I. Yudin et al., Phys. Rev. A 82, 011804(R)(2010)] that is a generalization
of Ramsey's method of separated oscillatory fields and consists of a sequence
of three excitation pulses. The pulse sequence is tailored to produce a
resonance signal which is immune to the light shift and other shifts of the
transition frequency that are correlated with the interaction with the probe
field. We investigate the scheme using a single trapped 171Yb+ ion and excite
the highly forbidden 2S1/2-2F7/2 electric-octupole transition under conditions
where the light shift is much larger than the excitation linewidth, which is in
the Hertz range. The experiments demonstrate a suppression of the light shift
by four orders of magnitude and an immunity against its fluctuations.Comment: 5 pages, 4 figure
Interrogation of caesium atoms in a fountain clock by a femtosecond laser microwave oscillator
A caesium fountain clock is operated utilizing a microwave oscillator that
derives its frequency stability from a stable laser by means of a fiber-laser
femtosecond frequency comb. This oscillator is based on the technology
developed for optical clocks and replaces the quartz based microwave oscillator
commonly used in fountain clocks. As a result, a significant decrease of the
frequency instability of the fountain clock is obtained, reaching 0.74E-14 at
100 s averaging time. We could demonstrate that for a significant range of
detected atom numbers the instability is limited by quantum projection noise
only, and that for the current status of this fountain clock the new microwave
source poses no limit on the achievable frequency instability.Comment: 4 pages, 4 figure
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