  Optical nanocavities for coherent interfaces usually have their electric
field maximum at the center point, which normally benefits interactions with
small local quantum emitters. Here, we propose a partial thickness modulation
on 2D slab photonic crystal cavities for a cratered cavity mode function to
improve nonlocal interactions. The thickness modulation is applied around the
central region, and has little effect on the fringe electric field, which
determines the coupling to waveguides or other cavities. Furthermore, the
partial modulation enhances the cratered electric field at positions that are
distant from the center point. Therefore, interactions with multiple separated
emitters are simultaneously enhanced, and the interaction with a large emitter
beyond the dipole approximation is also doubled. The improvement of the
nonlocal interactions demonstrates a great potential for the cratered cavity
mode profile for applications in quantum photonic networks.
