  We experimentally characterize Hopf bifurcation phenomena at femtojoule
energy scales in a multi-atom cavity quantum electrodynamical (cavity QED)
system, and demonstrate how such behaviors can be exploited in the design of
all-optical memory and modulation devices. The data are analyzed using a
semiclassical model that explicitly treats heterogeneous coupling of atoms to
the cavity mode. Our results highlight the interest of cavity QED systems for
ultra-low power photonic signal processing as well as for fundamental studies
of mesoscopic nonlinear dynamics.
