Entangled atoms for interferometry. Atoms, the building blocks of nature, can be used as extremely precise measurement devices. Since the 1960s, for example, our daily time has been defined by the internal oscillation frequency of the cesium atom, and realised by so-called atomic clocks. This internal oscillation frequency has to be converted to the clicks of a second. Even if the physical apparatus is not disturbed by technical or environmental noise, this frequency cannot be determined to arbitrary precision. There is a fundamental limit called shot noise limit if all atoms oscillate independently. Researchers at the Cluster of Excellence QUEST (Centre of Quantum Engineering and Space-Time Research) at Leibniz Universität Hannover, Germany, in collaboration with scientists from Spain, Italy and Denmark, now report in the journal Science that they have overcome this shot noise limit.