Optical trapping for a titanium atomic clock*

Titanium possesses narrow magnetic dipole (M1) and electric quadrupole (E2) transitions suitable for operation of an atomic clock at wavelengths in the fiber-optic telecommunications band. Design of the optical trapping potentials necessary for clock spectroscopy are complicated by the presence of large vector and tensor light shifts of the clock states. These lead to light shifts that depend on the polarization of the trapping light as well as the magnetic sublevel of the atoms. Here, we identify “magic” optical trapping conditions for several transitions in Ti such that there is no differential light shift between the lower and upper states, including these non-scalar effects. 

We previously reported a magneto-optical trap (MOT) of titanium atoms and recently implemented a second-stage MOT based on a narrow-line transition that results in a polarized atomic cloud. Following the narrow-line MOT, we will load atoms into an optical trap that is compatible with in-trap narrow-line Doppler cooling  while preserving the spin polarization of the atoms. After initial loading into the optical trap with in-trap cooling, the atoms can be transferred to a magic optical trap for precision spectroscopy of the clock transition. We identify magic conditions for both the magnetically insensitive, M1 clock transition between mJ=0 sublevels, as well as for magnetically sensitive transitions that can be used to calibrate systematic uncertainties relating to background fields and unambiguously measure the M1 and E2 transition moments of the clock transition.