  Two-dimensional photonic crystal membranes provide a versatile planar
architecture for integrated photonics to control the propagation of light on a
chip employing high quality optical cavities, waveguides, beamsplitters or
dispersive elements. When combined with highly non-linear quantum emitters,
quantum photonic networks operating at the single photon level come within
reach. Towards large-scale quantum photonic networks, selective dynamic control
of individual components and deterministic interactions between different
constituents are of paramount importance. This indeed calls for switching
speeds ultimately on the system's native timescales. For example, manipulation
via electric fields or all-optical means have been employed for switching in
nanophotonic circuits and cavity quantum electrodynamics studies. Here, we
demonstrate dynamic control of the coherent interaction between two coupled
photonic crystal nanocavities forming a photonic molecule. By using an
electrically generated radio frequency surface acoustic wave we achieve
optomechanical tuning, demonstrate operating speeds more than three orders of
magnitude faster than resonant mechanical approaches. Moreover, the tuning
range is large enough to compensate for the inherent fabrication-related cavity
mode detuning. Our findings open a route towards nanomechanically gated
protocols, which hitherto have inhibited the realization in all-optical
schemes.
