, ytterbium-173 (right) has a large nuclear spin and a strongly deformed nucleus whose strong fields interact with the electron shell. This turns forbidden quantum jumps into allowed transitions (see red-green arrow “slightly allowed”) and makes it easier to excite the transition with a laser. Credit: Physikalisch-Technische Bundesanstalt (PTB)“) Unlike other atoms (left), ytterbium-173 (right) has a large nuclear spin and a strongly deformed nucleus whose strong fields interact with the electron shell. This turns forbidden quantum jumps into allowed transitions (see red-green arrow "slightly allowed") and makes it easier to excite the transition with a laser. Credit: Physikalisch-Technische Bundesanstalt (PTB)

For many years, cesium atomic clocks have been reliably keeping time around the world. But the future belongs to even more accurate clocks: optical atomic clocks. In a few years’ time, they could change the definition of the base unit second in the International System of Units (SI). It is still completely open, which of the various optical clocks will serve as the basis for this.

Advances in optical atomic clocks

The large number of optical clocks that the Physikalisch-Technische Bundesanstalt (PTB), as a leading institute in this field, has realized could be joined by another type: an optical multi-ion clock with ytterbium-173 ions. It could combine the high accuracy of individual ions with the improved stability of several ions. This is the result of a cooperation between PTB and the Thai metrology institute NIMT.

The team led by Tanja Mehlstäubler reports on this in the current issue of the journal Physical Review Letters. The results are also interesting for quantum computing and, with a new look inside the atom, for fundamental research.

How optical atomic clocks work

Optical atomic clocks with single ions (such as ytterbium-171) are particularly accurate, while clocks with several particles (such as strontium atoms) are very stable. Tanja Mehlstäubler is researching a combination of these two properties and has already realized a multi-ion clock with indium. She is now also looking at ytterbium for the multi-ion idea, albeit a new isotope: ytterbium-173. "This isotope has a particularly interesting transition," explains the physicist.

Transition means the quantum leap in atomic clocks: the change of quantum state, which is only possible with a very specific frequency of microwave or laser radiation. Microwave radiation is used for the current cesium atomic clocks. Optical clocks work with laser radiation. Because these oscillations are around a hundred thousand times faster, time can be subdivided more finely and therefore measured more accurately.

Potential and implications of ytterbium-173 clocks

The quantum leap in the new ytterbium isotope leads to an excited state with a very long lifetime. "This allows us to make more stable measurements," explains first author Jialiang Yu. "But such transitions usually require strong laser light, which in turn can have major disadvantages."

However, this ytterbium isotope has a very specially shaped atomic nucleus and special properties that enabled the team to overcome the problems and even control several ions simultaneously.

This has now paved the way for a multi-ion optical ytterbium clock that combines the high accuracy of single-ion clocks with the improved stability of multi-ion operation. The new atomic species is also very well suited as a multi-qubit for quantum information, as the quantum states can be manipulated extremely precisely by laser radiation and more quantum information can be encoded simultaneously. This opens up a new possibility for quantum computer research.

Measuring the lifetime of the clock state for the first time provides valuable information about the structure of the atomic nucleus and enables sensitive tests of nuclear physics, for example for possible effects beyond the standard model of physics.

Publication details

Jialiang Yu et al, Nuclear Spin Quenching of the 2𝑆1/2→2𝐹7/2 Electric Octupole Transition in 173Yb+, Physical Review Letters (2026). DOI: 10.1103/fx1b-5666

Citation: Innovative optical atomic clock could combine single-ion accuracy with multi-ion stability (2026, January 21) retrieved 21 January 2026 from https://phys.org/news/2026-01-optical-atomic-clock-combine-ion.html

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