Research press release


Nature Physics

First field measurements using a portable atomic clock



今回、C Lisdatたちは、フランスアルプスの地下にある2.2 × 3 × 2.2 mのトレーラーの内部に携帯型原子時計を設置し、その挙動を、約100 km離れていて1000 m高度の低いイタリアの研究所にある原子時計の挙動と比較した。彼らは、フレジュス道路トンネルの中央という理想にはほど遠い現実的な条件で稼働する原子時計を用いて、山の中の研究所の高度を見積もり、これとは別の2種類の最先端の測地(「地球の形状」)測量法から得られた独立した測定結果とこの見積もりが一致することを示している。この測地測量法の1つは、衛星測位システムによる光学的な水準測量と重力場モデルを組み合わせたものである。


A portable atomic clock has been used to conduct field measurements for the first time, reports a study published online in Nature Physics this week. The transportable optical atomic clock was used to measure the height of a specific laboratory on a mountain in the Alps. The study represents a proof-of-principle demonstration for future applications of atomic clocks in gravitational measurements.

Atomic clocks are able to measure time to tremendously precise levels - one part in 1017. This sensitivity enables the detection of the infinitesimally small changes to the flow of time that general relativity predicts should take effect at different heights on Earth (owing to the varying strength of the gravitational field). This means that a very precise clock can be used as a gravity sensor. The high sensitivity of atomic clocks requires carefully controlled conditions, which are very difficult to create outside metrological labs.

Christian Lisdat and colleagues deployed a portable atomic clock fitted within a 2.2 × 3 × 2.2 m car trailer underground in the French Alps, and compared its bearings with those taken at a site in Italy - one roughly 100 km away and 1,000 m lower in height. Working in far from ideal, realistic conditions in the middle of the Frejus road tunnel, the authors used the atomic clock to estimate the height of the mountain laboratory and show that their estimate matches independent measurements made with two other state of the art geodetic (“shape of the earth”) measures: using optical spirit levelling satellite positioning systems combined with gravity field models.

The authors note that, although the precision of their measurement remains much lower than that achievable through conventional geodesy, by overcoming substantial technical challenges this measurement campaign is an important step towards the practical application of atomic clocks for geophysics.

doi: 10.1038/s41567-017-0042-3


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