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The European Physical Journal D

A cold atom clock in absence of gravity

Philippe Laurent, P. Lemonde, E. Simon, Giorgio Santarelli, Andr  Clairon, N. Dimarcq, P. Petit, C. Audoin, Ch Salomon

Published Jan 1, 1998• 66 citations
Publisher

Abstract

We describe the operation of a cold atom clock in reduced gravity. We have recorded the cesium hyperfine resonance signal at a frequency near 9.2 GHz in the gravity environment produced by jet plane parabolic flights. With a resonance width of 7 Hz, the device operated in a regime which is not accessible on earth. In the much lower gravity level of a satellite, our cold cesium clock would outperform the fountains with a potential accuracy of . This experiment paves the way to unprecedented performance in space applications such as tests of general relativity, global time dissemination, astronomy and geodesy.

DOI
10.1007/pl00021584

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We describe the operation of a cold atom clock in reduced gravity. We have recorded the cesium hyperfine resonance signal at a frequency near 9.2 GHz in the gravity environment produced by jet plane parabolic flights. With a resonance width of 7 Hz, the device operated in a regime which is not accessible on earth. In the much lower gravity level of a satellite, our cold cesium clock would outperform the fountains with a potential accuracy of . This experiment paves the way to unprecedented performance in space applications such as tests of general relativity, global time dissemination, astronomy and geodesy.
We describe a space cold atom clock prototype and its operation on board an aircraft. We have recorded the atomic resonance in zero gravity during parabolic flights. This experiment must be considered as an essential step toward the construction of a space clock using cold atoms. In a microgravity environment, a cold atomic clock would outperform all ground-based clocks. By the year 2002, we plan to operate a cold atom clock on board the international space station. This mission is called Atomic Clock Ensemble in Space (ACES). We have also performed a preliminary accuracy evaluation of the prototype. The interrogation of the cold atoms is performed inside a TE/sub 013/ cavity. On earth, the phase variations of the field induce a relative frequency shift of about 1/spl times/10/sup -13/. Although the frequency shift is expected to strongly decrease in microgravity, this cavity does not seem suitable for a 1/spl times/10/sup -16/ frequency uncertainty.
Improving global navigation satellite systems (GNSS) requires a more stable basis of timekeeping. Cold-atom clocks are currently the most accurate time references, but are large. This article presents an atomic clock, ``Rubiclock'', that is compact and portable, thanks to a fiber-based laser bench, isotropic light cooling, and atoms that remain motionless during the operating sequence. This configuration gives the clock an important benefit in microgravity; measurements performed on 0-ggg flights show better stability than on the ground. The stability that Rubiclock could achieve in a satellite makes it a good candidate for the next generation of GNSS.
Atomic clocks with cold atoms play important roles in the field of fundamental physics as well as primary frequency standards. Operating such cold atom clocks in space paves the way for further exploration in fundamental physics, for example dark matter and general relativity. We developed a space cold atom clock (SCAC), which was launched into orbit with the Space Lab TG-2 in 2016. Before it deorbited with TG-2 in 2019, the SCAC had been working continuously for almost 3 years. During the period in orbit, many scientific experiments and engineering tests were performed. In this article, we summarize the principle, development and in-orbit results. These works provide the basis for construction of a space-borne time-frequency system in deep space.
Summary form only given. The long observation times afforded by laser cooling of neutral atoms ushered in a new era of accuracy and stability for cesium atomic clocks. Traditional thermal beam atomic clocks are limited to interaction times of only a few milliseconds, while with laser cooling times of order 1 second have been realized with high stability. Most laser cooled clocks use a "fountain" geometry, in which the atoms are thrown up against the pull of gravity and realize longer times before falling back to the bottom of the apparatus. We have been developing a laser-cooling apparatus for flight on the International Space Station (ISS), with the intention of demonstrating linewidths of the cesium clock transition narrower than can be realized on the ground.
Atomic clocks based on laser-cooled atoms have made tremendous advances in both accuracy and stability. However, advanced clocks have not found their way into widespread use because there has been little need for such high performance in real-world/commercial applications. The drive in the commercial world favours smaller, lower-power, more robust compact atomic clocks that function well in real-world non-laboratory environments. Although the high-performance atomic frequency references are useful to test Einstein's special relativity more precisely, there are not compelling scientific arguments to expect a breakdown in special relativity. On the other hand, the dynamics of gravity, evidenced by the recent spectacular results in experimental detection of gravity waves by the LIGO Scientific Collaboration, shows dramatically that there is new physics to be seen and understood in space–time science. Those systems require strain measurements at less than or equal to 10 −20 . As we discuss here, cold atom optical frequency references are still many orders of magnitude away from the frequency stability that should be achievable with narrow-linewidth quantum transitions and large numbers of very cold atoms, and they may be able to achieve levels of phase stability, Δ Φ / Φ total ≤ 10 −20 , that could make an important impact in gravity wave science. This article is part of the themed issue ‘Quantum technology for the 21st century’.