Activities of time and frequency metrology at NICT: optical and microwave frequency standards and their remote comparisons

Ido, Tetsuya; Fujieda, M.; Hachisu, H.; Hayasaka, K.; Kajita, M.; Kumagai, M.; Li, Y.; Matsubara, K.; Nagano, S.; Ohtsubo, N.; Hanado, Y.; Hosokawa, M.

National Institute of Information and Communications Technology (NICT, Tokyo) has been conducting research, development, and public service on various area of ICT. One of these activities is found in the area of time and frequency standards, where NICT provides the national frequency standard and the Japan Standard Time. Besides that, atomic frequency standards, including cesium fountains, a calcium ion clock, a strontium (Sr) lattice clock, and an indium ion clock, are also studied. This poster contribution briefly summarizes the current status and frequency comparisons of these frequency standards.

We also study the technology to make remote comparison of these standards against others developed in external institutes. Sr lattice clock offers a convenient platform for this purpose because nearly ten Sr - based clocks are available in worldwide including the one in NICT with uncertainty of 8.610^-17. In 2011, fiber link to University of Tokyo was established with the base line of 24 km, whereas that with a long baseline to PTB was realized in 2013 by a two-way satellite link using the carrier-phase. The former revealed the gravitational redshift caused by the elevation difference of 56 m with uncertainty of 7 m. On the other hand, the latter for the first time realized direct comparison of two optical clocks in intercontinental scale. The frequency agreement between Japan and Europe was confirmed on that occasion with the uncertainty of 1.610^-15, and further efforts are ongoing to reduce the uncertainty and instability.

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