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In this article, the interest of space environment for cold atoms is outlined. After a brief review of cooling techniques and Bose–Einstein condensation, the case of atomic clocks in microgravity is discussed. The scientific objectives of the European mission ACES are presented. ACES will fly onboard the international space station in 2005–2006.

Recently, microwave phase gradients were identified as the main source of uncertainty in the continuous fountain clock. Indeed, because of its particular geometry with two interaction zones, a dedicated research effort was necessary to reduce this effect. With the help of 3D finite element simulations and ultra-precise machining, we report here on the design and realization of a new kind of low phase gradient microwave cavity. The proposed geometry based on a ring waveguide of rectangular cross-section has a theoretical spatial phase variation of 30 μrad over the interaction zones, which corresponds to a predicted relative frequency shift below 10-15.

METAS is the Swiss Federal Office of Metrology and Accreditation, the METAS time & frequency laboratory (T&F Lab) operates a cesium primary standard, maintains the Swiss national time scales, disseminates precise time and performs calibrations for customers. This paper reports current activities in the laboratory

This paper presents a study of the transfer of frequency stability from an atomic reference to a quartz-crystal oscillator. The study is done for the cases of active and passive atomic frequency standards in which one makes use of a phase-lock loop and of a frequency-lock loop, respectively. The analysis is made in both the frequency and time domains and covers the cases of the hydrogen and rubidium masers and the passive cesium-and rubidium-frequency standards. The results obtained from numerical calculations are presented under the form of graphs. These results include the fractional frequency spectral density Sy(f) as a function of the Fourier frequency f, and the two sample variance ?2(?) as a function of ?, the sampling time.

This paper presents a study of the transfer of frequency stability from an atomic reference to a quartz-crystal oscillator. The study is done for the cases of active and passive atomic frequency standards in which one makes use of a phase-lock loop and of a frequency-lock loop, respectively. The analysis is made in both the frequency and time domains and covers the cases of the hydrogen and rubidium masers and the passive cesium-and rubidium-frequency standards. The results obtained from numerical calculations are presented under the form of graphs. These results include the fractional frequency spectral density Sy(f) as a function of the Fourier frequency f, and the two sample variance ?2(?) as a function of ?, the sampling time.