Fast Scramblers, Horizons and Expander Graphs
  We propose that local quantum systems defined on expander graphs provide a simple microscopic model for thermalization on quantum horizons. Such systems are automatically fast scramblers and are motivated from the membrane paradigm by a conformal transformation to the so-called optical metric. 
Jose L.F. Barbon and Javier M. Magan
hep-th gr-qc quant-ph