Measurement of the electric quadrupole moment of the 4d2D5/2 level in 88Sr+.

The quadrupole moment of the 4d (2)D(5/2) level in 88Sr+ has been measured to be 2.6(3)ea(2)(0), where a(0) is the Bohr radius and e the elementary charge. A single laser-cooled strontium ion was confined in an end cap trap with a variable dc quadrupole potential, and measurements were made on the 5s (2)S(1/2)-4d (2)D(5/2) transition at 674 nm using a femtosecond optical frequency comb. This work shows that measurements of the unperturbed 88Sr+ transition frequency with sub-Hz uncertainty are possible and is important in understanding the reproducibility of ion trap optical frequency standards.