arXiv subjects

A. Godone

Publications and source records attributed to A. Godone.

4 recordsLinked to original sources

arXiv2014

Coherent optical frequency transfer at 5e-19 over a doubled 642 km fiber link

To significantly improve the frequency references used in radio-astronomy and precision measurements in atomic physics, we provide frequency dissemination through a 642 km coherent optical fiber link, that will be also part of a forthcoming European network of optical links. We obtained a resolution of 3e-19 at 1000 s on the frequency transfer, and an accuracy of 5e-19. The ultimate link performance has been evaluated by doubling the link to 1284 km, demonstrating a new characterization technique based on the double round-trip on a single fiber. The arming of a second fiber is avoided: this is beneficial to long hauls realizations in view of a continental fiber network for frequency and time metrology. The data analysis is based on the Allan deviation; its expression is theoretically derived for the observed noise power spectrum, which is seldom found in the literature.

physics.optics↗

arXiv2014

Beyond the fundamental noise limit in coherent optical fiber links

It is well known that temperature variations and acoustic noise affect ultrastable frequency dissemination along optical fiber. Active stabilization techniques are in general adopted to compensate for the fiber-induced phase noise. However, despite this compensation, the ultimate link performances remain limited by the so called delay-unsuppressed fiber noise that is related to the propagation delay of the light in the fiber. In this paper, we demonstrate a data post-processing approach which enables us to overcome this limit. We implement a subtraction algorithm between the optical signal delivered at the remote link end and the round-trip signal. In this way, a 6 dB improvement beyond the fundamental limit imposed by delay-unsuppressed noise is obtained. This result enhances the resolution of possible comparisons between remote optical clocks by a factor of 2. We confirm the theoretical prediction with experimental data obtained on a 47 km metropolitan fiber link, and propose how to extend this method for frequency dissemination purposes as well.

physics.optics↗

arXiv2003

Black Body Radiation Shift of the 133Cs Hyperfine Transition Frequency

We report the theoretical evaluations of the static scalar polarizability of the 133Cs ground state and of the black body radiation shift induced on the transition frequency between the two hyperfine levels with m_F = 0. This shift is of fundamental importance in the evaluation of the accuracy of the primary frequency standards based on atomic fountains and employed in the realization of the SI second in the International Atomic Time (TAI) scale at the level of 1e-15. Our computed value for the polarizability is alpha_0=6.600(16)e-39 Cm^2/V in agreement at the level of 1e-3 with recent theoretical and experimental values. As regards the black body radiation shift we .nd for the relative hyper.ne transition frequency beta=-1.49 (7)e-14 at T = 300 K in agreement with frequency measurements reported by our group and by Bauch and Schroder [Phys. Rev. Lett. 78, 622, (1997)]. This value is lower by 2e-15 than that obtained with measurements based on the dc Stark shift and than the value commonly accepted up to now.

physics.atom-ph↗

arXiv2003

Measurement of the Blackbody Radiation Shift of the 133Cs Hyperfine Transition in an Atomic Fountain

We used a Cs atomic fountain frequency standard to measure the Stark shift on the ground state hyperfine transiton frequency in cesium (9.2 GHz) due to the electric field generated by the blackbody radiation. The measures relative shift at 300 K is -1.43(11)e-14 and agrees with our theoretical evaluation -1.49(07)e-14. This value differs from the currently accepted one -1.69(04)e-14. The difference has a significant implication on the accuracy of frequency standards, in clocks comparison, and in a variety of high precision physics tests such as the time stability of fundamental constants.

physics.atom-ph↗