Measurement of the electric quadrupole moment of the 4d D5/22 level in Sr+88

The quadrupole moment of the 4d D5/22 level in Sr+88 has been measured to be 2.6(3)ea02, where a0 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 S1/22-4d D5/22 transition at 674 nm using a femtosecond optical frequency comb. This work shows that measurements of the unperturbed Sr+88 transition frequency with sub-Hz uncertainty are possible and is important in understanding the reproducibility of ion trap optical frequency standards