Coulomb coupling between two nanospheres trapped in a bichromatic optical tweezer

Levitated optomechanics is entering the multiparticle regime, paving the way for the use of arrays of strongly coupled massive oscillators to explore complex interacting quantum systems. Here, we demonstrate the trapping of two nanospheres inside a dual optical tweezer generated by two copropagating lasers operating at different wavelengths (1064 nm and 976 nm). Due to the chromatic aberration of the tweezer optics, two focal points are created approximately 9 microns apart, each one acting as an optical trap for a silica nanoparticle. At this distance, the surface charges on the nanospheres produce a Coulomb force that couples their motion along the tweezer axis. The strong coupling regime is achieved, as evidenced by the observed avoided crossing of the normal-mode frequencies. These results highlight the potential of our experimental scheme for future studies on systems of strongly coupled oscillators, including their implementation in optical cavities, both in the classical and in quantum regime.