Different atoms and ions possess characteristic energy levels – like a fingerprint they are unique for each species. Among them, the atomic ion 173Yb+ has attracted growing interest because of its particularly rich energy structure, which is promising for applications in quantum technologies and searches for so-called new physics. On the flip side, the complex structure that makes 173Yb+ interesting has long prevented detailed investigations of this ion.
Now, researchers from PTB, TU Braunschweig, and the University of Delaware took a closer look at the ion's energy structure. To achieve this, they trapped a single 173Yb+ ion and developed methods for preparing and detecting its energy state despite the complicated energy structure. This enabled high-resolution laser and microwave spectroscopy.
In particular, the researchers investigated energy shifts arising from interactions between the nucleus and its surrounding electrons, also called hyperfine structure. Combined with first-principle theory calculations, the precise measurement results yielded new information about the ion's nucleus.
Though the tiny atomic nucleus is often imagined as a charged, point-like particle, in reality it can have a complicated structure that is hard to investigate directly. Here, the electrons were used as a magnifying glass, allowing to investigate the structure of the nucleus indirectly. In particular, the combination of experiment and theory illuminates how the magnetic field of the nucleus is distributed across its volume. To achieve this, the researchers also performed comparison measurements with the 171Yb+ -isotope, which has a different nuclear structure but the same electron shell.
"Our measurements show that even very subtle properties of the atomic nucleus can be accessed through the surrounding electron cloud," explains Dr. Jian Jang of PTB. "This not only leads to a better understanding of this particular nucleus, but also provides an important experimental foundation for using complex ions such as 173Yb+ for highly precise clocks and for tests of fundamental physics in the future."
Scientific Publication:
J. Jiang, A. V. Viatkina, Saaswath JK, M. Steinel, M. Filzinger, E. Peik, S. G. Porsev, M. S. Safronova, A. Surzyhkov, and N. Huntemann: High-resolution spectroscopy of 173Yb+ ions, Phys. Rev. Lett. 136, 023001 (2026) . https://doi.org/10.1103/rcdh-s4d7
