Precision laser spectroscopy without optical detection Forbidden transitions in highly charged ions

Laser spectroscopy of trapped ions is likely to be limited by the availability of suitable detection systems for fluorescence photons, especially in the infrared transition frequency domain. This restriction can be circumvented when ions are stored in a Penning trap with an additional magnetic field inhomogeneity which couples the ion oscillation frequencies to the oscillation energies in a well-defined way. In such a case, laser cooling (or heating) on the optical transition of interest can be detected electronically by a corresponding shift of the ion oscillation frequency. Thereby, the transition of interest can be determined with high accuracy using only a single stored ion and in absence of any optical detection system.