  We show that atoms subject to laser radiation may form a non-additive
many-body system on account of their long-range forces, when the atoms are
trapped in the vicinity of a fiber with a Bragg grating. When the laser
frequency is inside the grating's bandgap but very close to its edge, we find
that the range and strength of the laser-induced interaction becomes
substantially enhanced, due to the large density of states near the edge, while
the competing process of scattering to the fiber is inhibited. The dynamics of
the atomic positions in this system conforms to a prominent model of
statistical physics which exhibits slow relaxation. This suggests the
possibility of using laser-illuminated atoms to study the characteristics of
non-additive systems.
