Mixing of 0+ and 0- observed in the hyperfine and Zeeman structure of ultracold Rb2 molecules

Abstract

Westudy the combination of the hyperfine and Zeeman structure in the spin-orbit coupled A1 ∑u - bπu complex of 87Rb2. For this purpose, absorption spectroscopy at a magnetic field around B = 1000 Gis carried out.We drive optical dipole transitions fromthe lowest rotational state of an ultracold Feshbachmolecule to various vibrational levelswith 0+ symmetry of the A - b complex. In contrast to previous measurements with rotationally excited alkali-dimers, we do not observe equal spacings of the hyperfine levels. In addition, the spectra vary substantially for different vibrational quantum numbers, and exhibit large splittings of up to 160 MHz, unexpected for 0+ states. The level structure is explained to be a result of the repulsion between the states 0+ and 0- of b3 πu, coupled via hyperfine and Zeeman interactions. In general, 0? and 0+ have a spin-orbit induced energy spacing Δ, that is different for the individual vibrational states. From each measured spectrum we are able to extract Δ, which otherwise is not easily accessible in conventional spectroscopy schemes.Weobtain values of ? in the range of ± 100 GHzwhich can be described by coupled channel calculations if a spinorbit coupling is introduced that is different for 0? and 0+ of b3 πu.