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Systematic frequency shifts in linear ion chains of a few 10−19 achievable


Some of the currently most accurate optical clocks are based on trapped ions since they allow excellent control over systematic frequency shifts. To benefit from further reductions in the frequency uncertainty in practice, the averaging times of the next generation of trapped-ion clocks will, however, also have to be reduced. Researchers at the QUEST Institute of PTB have succeeded in demonstrating that taking the step from one to several trapped ions in a clock is not contradictory to lower frequency uncertainties.

Visualization of the simultaneously measured micromotion amplitudes in a crystal of 14 trapped ytterbium ions spanning a length of approx. 400 μm. Within a recently developed high-precision ion trap, it was possible to reduce the resulting time dilation shift to less than 10−19.

Taking this step has become possible thanks to precision ion traps that were developed at PTB and allow relative systematic uncertainties of a few 10−19 to be achieved. Among other investigations, the micromotion of trapped ions was measured with nanometer resolution using a novel temporally and spatially resolved detection method. With this new method, the researchers were able to show that the micromotion-induced frequency shifts of every individual ion inside a linear crystal can be kept in the sub-mHz range. The results open up the path for novel ion clock concepts such as the use of entangled quantum states and the simultaneous operation of several clocks on a single chip.