Artificial light and quantum order in systems of screened dipoles
  The origin of light is a unsolved mystery in nature. Recently, it was suggested that light may originate from a new kind of order - quantum order. To test this idea in experiments, we study systems of screened magnetic/electric dipoles in 2D and 3D lattices. We show that our models contain an artificial light -- a photon-like collective excitation. We discuss how to design realistic devices that realize our models. We show that the ``speed of light'' and the ``fine structure constant'' of the artificial light can be tuned in our models. The properties of artificial atoms (bound states of pairs of artificial charges) are also discussed. The existence of artificial light (as well as artificial electron) in condensed matter systems suggests that elementary particles, such as light and electron, may not be elementary. They may be collective excitations of quantum order in our vacuum. Our models further suggest that a gauge theory is a string-net theory in disguise. Light is a fluctuation of nets of large closed strings and charge is the end of open strings. 
Xiao-Gang Wen