Dissipation-induced optical nonlinearity at low light levels. (arXiv:1108.4730v1 [physics.optics])

Dissipation-induced optical nonlinearity at low light levels. (arXiv:1108.4730v1 [physics.optics]):
We observe a dissipation-induced nonlinear optical process in a gas of cold
atoms that gives rise to large nonlinear coupling strengths with high
transparency. The nonlinearity results from the simultaneous cooling and
crystallization of the gas, and can give rise to efficient Bragg scattering in
the form of a six-wave-mixing process at low-light-levels with an extremely
large effective fifth-order nonlinear susceptibility of \chi^(5)= 7.6 x 10-15
(m/V)^4. For large optical gains, collective scattering due to the strong
light-matter coupling leads to slow group velocities (~c/105) and long atomic
coherence times (~100 {\mu}s).