ac Stark effect in ultracold polar 87Rb133Cs molecules

We investigate the effect of far-off-resonant trapping light on ultracold bosonic (RbCs)-Rb-87-Cs-133 molecules. We use kHz-precision microwave spectroscopy to measure the differential ac Stark shifts between the ground and first excited rotational levels of the molecule with hyperfine-state resolution. We demonstrate through both experiment and theory that coupling between neighboring hyperfine states manifests in rich structure with many avoided crossings. This coupling may be tuned by rotating the polarization of the linearly polarized trapping light. A combination of spectroscopic and parametric heating measurements allows complete characterization of the molecular polarizability at a wavelength of 1550 nm in both the ground and first excited rotational states.