Isotope-selective trapping of rare calcium ions using high-power incoherent light sources for the second step of photo-ionization

摘要

Rare calcium isotope ~(48)Ca~+ (0.187%) has been selectively loaded in a linear Paul trap using two ultraviolet light emitting diodes with the output power of 85 mW for the second excitation in a two-step photo-ionization process. Isotope selectivity has been achieved by utilizing the isotope shifts for the 4s~2 ~1S_0-4s4p ~1P_1 transition of neutral calcium atom. Sympathetic cooling of ~(48)Ca~+ ions has been demonstrated using ~(40)Ca~+ ions as refrigerant ions. Purification of rare isotope ~(42)Ca~+ ions (0.647%) from a mixture of ~(40)Ca~+ (96.9%) and ~(42)Ca~+ ions has been performed by adjusting the detuning of the cooling laser frequency, which overcomes the imperfect selectivity for some rare isotopes having close resonance frequencies to that of ~(40)Ca in the 4s~2 ~1S_0-4s4p ~1P_1 transition. The methods can be applied to ~(43)Ca~+ ion (0.135%) that has been considered as one of the attractive candidates for quantum information processing as well as for an optical frequency standard.