Polarizability of ultracold Rb2 molecules in the rovibrational ground state of a3Σu+

Abstract

We study, both theoretically and experimentally, the dynamical polarizability α (ω) of 2 molecules in the rovibrational ground state of a3Σu+. Taking all relevant excited molecular bound states into account, we compute the complex-valued polarizability α (ω) for wave numbers up to 20 000 cm-1. Our calculations are compared to experimental results at 1064.5 nm (∼ 9400 cm-1) as well as at 830.4 nm (∼12 000 cm-1). Here, we discuss the measurements at 1064.5 nm. The ultracold Rb2 molecules are trapped in the lowest Bloch band of a 3D optical lattice. Their polarizability is determined by lattice modulation spectroscopy which measures the potential depth for a given light intensity. Moreover, we investigate the decay of molecules in the optical lattice, where lifetimes of more than 2 s are observed. In addition, the dynamical polarizability for the X1Σg+ state is calculated. We provide simple analytical expressions that reproduce the numerical results for α (ω) for all vibrational levels of a3Σu+ as well as X1Σg+. Precise knowledge of the molecular polarizability is essential for designing experiments with ultracold molecules as lifetimes and lattice depths are key parameters. Specifically the wavelength at ∼1064 is of interest, since here, ultrastable high power lasers are available.