  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.
