We report on a conceptually new test of the equivalence principle performed by measuring the acceleration in Earth's gravity field of two isotopes of strontium atoms, namely, the bosonic (88)Sr isotope which has no spin versus the fermionic (87)Sr isotope which has a half-integer spin. The effect of gravity on the two atomic species has been probed by means of a precision differential measurement of the Bloch frequency for the two atomic matter waves in a vertical optical lattice. We obtain the values η=(0.2±1.6)×10(-7) for the Eötvös parameter and k=(0.5±1.1)×10(-7) for the coupling between nuclear spin and gravity. This is the first reported experimental test of the equivalence principle for bosonic and fermionic particles and opens a new way to the search for the predicted spin-gravity coupling effects.
To significantly improve the frequency references used in radio-astronomy and the precision measurements in atomic physics, we provide frequency dissemination through a 642-km coherent optical fiber link.\ud
On the frequency transfer, we obtained a frequency instability of 3x10^-\ud
19\ud
at 1,000 s in terms of Allan deviation on a 5-mHz measurement bandwidth, and an accuracy of 5x10^-19. The ultimate link performance has been evaluated by doubling the link to 1,284 km, demonstrating a new characterization technique based on the double round\ud
trip on a single fiber. This method is an alternative to\ud
previously demonstrated techniques for link characterization. In particular, the use of a single fiber may be beneficial to long hauls realizations in view of a continental fiber network for frequency and time metrology, as it avoids the doubling of the amplifiers, with a subsequent reduction in costs and maintenance. A detailed analysis of the results is presented, regarding the phase noise, the cycle-slips detection and removal and the instability evaluation. The observed noise power spectrum is seldom found in the literature; hence, the expression of the Allan\ud
deviation is theoretically derived and the results confirm the expectations
We describe a frequency-stabilized diode laser at 698 nm used for high-resolution spectroscopy of the 1 S 0 -3 P 0 strontium clock transition. For the laser stabilization we use state-of-the-art symmetrically suspended optical cavities optimized for very low thermal noise at room temperature. Two-stage frequency stabilization to high-finesse optical cavities results in measured laser frequency noise about a factor of three above the cavity thermal noise between 2 Hz and 11 Hz. With this system, we demonstrate high-resolution remote spectroscopy on the 88 Sr clock transition by transferring the laser output over a phase noisecompensated 200-m-long fiber link between two separated laboratories. Our dedicated fiber link ensures a transfer of the optical carrier with frequency stability of 7 × 10 −18 after 100 s integration time, which could enable the observation of the strontium clock transition with an atomic Q of 10 14 . Furthermore, with an eye toward the development of transportable optical clocks, we investigate how the complete laser system (laser + optics + cavity) can be influenced by environmental disturbances in terms of both short-and long-term frequency stability.
We experimentally study two Ti:sapphire optical frequency comb femtosecond regimes, respectively, with a linear and a nonlinear dependence of the carrier-envelope offset frequency (f CEO ) on pump intensity. For both regimes, we study the effect of single-and multimode pump lasers on the f CEO phase noise. We demonstrate that the femtosecond regime is playing a more important role on the f CEO phase noise and stability than the pump laser type.
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