Polarisation-dependent optical pumping for interrogation of a magnetic-field-independent “clock” transition in laser-cooled trapped 87Sr+

Abstract.

We discuss the prospect of using the ⁸⁷Sr⁺ ion as an optical frequency standard. The ion offers a narrow electric quadrupole clock transition which has no first-order Zeeman shifts, and the required wavelengths can be generated with convenient solid-state laser systems. We describe how to cool and probe the ion in zero magnetic field by employing polarisation modulation of the cooling light to avoid coherent population trapping in dark states. The polarisation modulation scheme also provides optical pumping of the ion into the initial state of the narrow clock transition.