Precision spectroscopy with a single 40Ca+ ion in a Paul trap*
Guan Huaa),b), Huang Yaoa),b), Liu Pei-Lianga),b), Bian Wua),b),c), Shao Hua),b),c), Gao Ke-Lina),b)†
       
(a) 6 Hz linewidth of one component with Δ m j = 0; (b) the relative fractional stability of two independent 40Ca+ optical frequency standards.