Scientists at the Physikalisch-Technische Bundesanstalt (PTB) in Germany have developed a groundbreaking new type of optical atomic clock known as the ion crystal clock. This innovation has the potential to measure time and frequency with 1,000 times greater accuracy than the cesium clocks currently used to define the SI second. The next generation of atomic clocks operates using laser frequencies, which “tick” approximately 100,000 times faster than the microwave frequencies used in today’s cesium clocks.
Although optical clocks are still under evaluation, some have already proven to be 100 times more accurate than cesium-based clocks. In an optical atomic clock, atoms are irradiated by laser light. If the laser has the correct frequency, the atoms change their quantum-mechanical state.
For this purpose, the atoms have to be shielded from any external influences – and remaining influences must be measured accurately. To date, these clocks have been operated with one individual clock ion. Its weak signal must be measured over long periods of time – up to two weeks – in order to measure the frequency with such a low uncertainty.
Advancing timekeeping with ion crystals
The newly developed clock will drastically shorten this measuring time by parallelizing: Multiple ions – often of different kinds – will be simultaneously trapped in one trap. By interacting, they form a new, crystalline structure.
In addition, this concept allows the strengths of different types of ions to be combined,” explains PTB physicist Jonas Keller. “We use indium ions as they have favorable properties to achieve high accuracy. For efficient cooling, ytterbium ions are added to the crystal.”
The clock currently reaches an accuracy close to the 18th decimal place.
Two further optical and one microwave clock systems of PTB participated in the comparisons: a single-ion ytterbium clock, a strontium lattice clock, and a cesium fountain clock. The ratio of the indium clock to the ytterbium clock is the first to reach an overall uncertainty lower than the limit required for such comparisons by the roadmap for the redefinition of the second. The concept promises a new generation of highly stable and accurate optical ion clocks.
It is also applicable to other types of ions and opens up new opportunities for entirely new clock concepts such as the use of quantum many-body states or the cascaded interrogation of several ensembles. This development in ion clock technology represents a significant step towards advancing timekeeping precision, which could have wide-ranging implications for scientific research and technology.
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