Lieb-Robinson bounds and the speed of light from topological order

Understand

We apply the Lieb-Robinson bounds technique to find the maximum speed of interaction in a spin model with topological order whose low-energy effective theory describes light [see X.-G.

• Wen, \prb {\bf 68}, 115413 (2003)].
• The maximum speed of interactions is found in two dimensions is bounded from above less than $\sqrt{2} e$ times the speed of emerging light, giving a strong indication that light is indeed the maximum speed of interactions.
• This result does not rely on mean field theoretic methods.