Damped Rabi oscillations of a cold trapped ion

We demonstrate that the recently observed damping of Rabi oscillations of a trapped ${}^9{\mathrm{Be}}^{+}$ ion initially cooled to its motional ground state [Meekhof et al., Phys. Rev. Lett. 76, 1796 (1996)] is caused by quantum jumps to an auxiliary electronic state. This mechanism also predicts an asymmetric decay of the electronic-state population that is found to be in good agreement with the measured data.