  The interaction between quantum two-level systems is typically short-range in
free space and most photonic environments. Here we show that diminishing
momentum isosurfaces with equal frequencies can create a significantly extended
range of interaction between distant quantum systems. The extended range is
robust and does not rely on a specific location or orientation of the
transition dipoles. A general relation between the interaction range and
properties of the isosurface is described for structured photonic media. It
provides a new way to mediate long-range quantum behavior.
