Laser spectroscopy by a radiofrequency measurement on a single ion in a Penning trap

We present a novel concept for precision laser spectroscopy on a single ion confined in a Penning trap. This concept circumvents the need for detection of fluorescence photons. Instead, changes in motional frequencies of the trapped ion are used to determine atomic transitions of interest with relative accuracies better than 10(-10). We discuss the application to a measurement of forbidden transitions in highly charged ions, making stringent tests of bound-state quantum electrodynamics (QED) calculations, including the nuclear recoil contribution, possible. The method may also be used to 'weigh' optical excitations in light ions by the relativistic frequency shift.