Construction of spin models displaying quantum criticality from quantum   field theory
  We provide a method for constructing finite temperature states of one-dimensional spin chains displaying quantum criticality. These models are constructed using correlators of products of quantum fields and have an analytical purification. Their properties can be investigated by Monte-Carlo simulations, which enable us to study the low-temperature phase diagram and to show that it displays a region of quantum criticality. The mixed states obtained are shown to be close to the thermal state of a simple nearest neighbour Hamiltonian. 
Ivan Glasser, J. Ignacio Cirac, Germ\'an Sierra, Anne E. B. Nielsen
cond-mat.str-el cond-mat.stat-mech quant-ph