115 research outputs found
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
A coherent optical link through the turbulent atmosphere
We describe the realization of a 5 km free space coherent optical link
through the turbulent atmosphere between a telescope and a ground target. We
present the phase noise of the link, limited mainly by atmospheric turbulence
and mechanical vibrations of the telescope and the target. We discuss the
implications of our results for applications, with particular emphasis on
optical Doppler ranging to satellites and long distance frequency transfer.Comment: version 2, modified following comments from colleagues and reviewer
I.C.E.: a Transportable Atomic Inertial Sensor for Test in Microgravity
We present our the construction of an atom interferometer for inertial
sensing in microgravity, as part of the I.C.E. (\textit{Interf\'{e}rom\'{e}trie
Coh\'{e}rente pour l'Espace}) collaboration. On-board laser systems have been
developed based on fibre-optic components, which are insensitive to mechanical
vibrations and acoustic noise, have sub-MHz linewidth, and remain frequency
stabilised for weeks at a time. A compact, transportable vacuum system has been
built, and used for laser cooling and magneto-optical trapping. We will use a
mixture of quantum degenerate gases, bosonic Rb and fermionic K,
in order to find the optimal conditions for precision and sensitivity of
inertial measurements. Microgravity will be realised in parabolic flights
lasting up to 20s in an Airbus. We show that the factors limiting the
sensitivity of a long-interrogation-time atomic inertial sensor are the phase
noise in reference frequency generation for Raman-pulse atomic beam-splitters
and acceleration fluctuations during free fall
Evaluation of Doppler Shifts to Improve the Accuracy of Primary Atomic Fountain Clocks
We demonstrate agreement between measurements and ab initio calculations of
the frequency shifts caused by distributed cavity phase variations in the
microwave cavity of a primary atomic fountain clock. Experimental verification
of the finite element models of the cavities gives the first quantitative
evaluation of this leading uncertainty and allows it to be reduced to delta nu
/ nu = 8.4\times10^-17. Applying these experimental techniques to clocks with
improved microwave cavities will yield negligible distributed cavity phase
uncertainties, less than \pm1\times10^-17.Comment: To appear in PR
Tests of relativity using a microwave resonator
The frequencies of a cryogenic sapphire oscillator and a hydrogen maser are
compared to set new constraints on a possible violation of Lorentz invariance.
We determine the variation of the oscillator frequency as a function of its
orientation (Michelson-Morley test) and of its velocity (Kennedy-Thorndike
test) with respect to a preferred frame candidate. We constrain the
corresponding parameters of the Mansouri and Sexl test theory to and which is equivalent to the best previous result for the
former and represents a 30 fold improvement for the latter.Comment: 8 pages, 2 figures, submitted to Physical Review Letters (October 3,
2002
Long-distance frequency dissemination with a resolution of 10-17
We use a new technique to disseminate microwave reference signals along
ordinary optical fiber. The fractional frequency resolution of a link of 86 km
in length is 10-17 for a one day integration time, a resolution higher than the
stability of the best microwave or optical clocks. We use the link to compare
the microwave reference and a CO2/OsO4 frequency standard that stabilizes a
femtosecond laser frequency comb. This demonstrates a resolution of 3.10-14 at
1 s. An upper value of the instability introduced by the femtosecond
laser-based synthesizer is estimated as 1.10-14 at 1 s
An agile laser with ultra-low frequency noise and high sweep linearity
We report on a fiber-stabilized agile laser with ultra-low frequency noise.
The frequency noise power spectral density is comparable to that of an
ultra-stable cavity stabilized laser at Fourier frequencies higher than 30 Hz.
When it is chirped at a constant rate of ~ 40 MHz/s, the max non-linearity
frequency error is about 50 Hz peak-to-peak over more than 600 MHz tuning
range. The Rayleigh backscattering is found to be a significant frequency noise
source dependent on fiber length, chirping rate and the power imbalance of the
interferometer arms. We analyze this effect both theoretically and
experimentally and put forward techniques to reduce this noise contribution.Comment: 14 pages, 11 figures, accepted by Optics Expres
Contributing to the International Atomic Time Using an Atomic Rb Fountain Clock
International audienc
Contributing to the International Atomic Time Using an Atomic Rb Fountain Clock
International audienc
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