On January 3, our article entitled “Penning-trap eigenfrequency measurements with optical radiofrequency detectors” by J. Berrocal, A. Hernández, I. Arrazola, F. Domínguez, A. Carrasco-Sanz, F. J. Fernández, M. Block, and D. Rodríguez was published in the journal Physical Review Research.

Link to the publication: https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.6.L012001

In this work we determine directly all the eigenfrequencies of a single laser-cooled ion in a Penning trap through optical detection and perform cyclotron-frequency comparisons between calcium isotopes with kinetic temperatures in the order of a millikelvin. Such a method makes the frequency measurements more robust against inhomogeneities of the magnetic field and deviations of the electric quadrupole field due to mechanical imperfections of the trap.