Geometric Entropy, Wave Functionals, and Fermions
  We develop techniques for calculating the ground state wave functional and the geometric entropy for some simple field theories. Special attention is devoted to fermions, which present special technical difficulties in this regard. Explicit calculations are carried through for free mass bosons and fermions in two dimensions, using an adaptation of Unruh's technique to treat black hole radiance. 
Finn Larsen and Frank Wilczek