Measurement of the ⁸⁷Rb D-line vector tune-out wavelength

A tune-out wavelength characterizes a zero in the electric polarizability of the atom, such that the atom experiences no first-order energy shift in the presence of the light. Tune-out wavelength measurements are useful for experiments involving multiple species, and for providing precise constraints on the electric dipole moments of the atom. The location of a tune-out wavelength depends in general on the polarization state of the light, and this dependence is characterized by the vector polarizability. To date, precise measurements have focused on the polarization-independent scalar polarizability, but we report here a vector measurement using circularly polarized light. For an estimated polarization purity of 0.9931(1), we find a tune-out wavelength for ⁸⁷Rb at 785.1522(3) nm. The experimental result agrees with theoretical expectations when small contributions from the core electrons and off-resonant alence states are taken into account. This type of measurement can provide information about the dipole matrix elements which is particularly applicable to the interpretation of atomic parity violation experiments.