Spectra of 4²S_1/2→3²D_5/2 Transitions of a Single Trapped ⁴⁰Ca⁺ Ion

We investigate the spectra of the electric quadrupole 4²S_1/2→3²D_5/2 transitions in a single ⁴⁰Ca⁺ ion confined in a home-built linear trap. We probe the transitions with an ultra-narrow bandwidth laser at 729 nm. In a weak magnetic field, the quadrupole transition splits into ten components with the maximal line strength proportional to their squared Clebsch–Gordan factors. In a magnetic field of the order of Gauss, the observed equidistant sideband reflects the Zeeman substructure modulated by the quantized oscillation due to the secular motion in the trap. The temperature of the trapped ion can be determined by the envelope of the sideband spectrum. We also demonstrate the Rabi oscillation in a carrier transition after the ion has been Doppler cooled, which can be fitted by the model with the thermal state of motion.