Direct frequency-comb spectroscopy of a dipole-forbidden clock transition in trapped ~(40)Ca~(+) ions

摘要

We demonstrate direct frequency-comb (FC) spectroscopy of the dipole-forbidden 4s~(2)S_(1/2)-3d~(2)D_(5/2) transition in trapped ~(40)Ca~(+) ions using an unamplified FC laser. The excitation is detected with nearly 100percent efficiency using a shelving scheme in combination with single-ion imaging. The method demonstrated here has the potential to reach hertz-level accuracy, if a hertz-level linewidth FC is used in combination with confinement in the Lamb-Dicke regime.