Thermal Pure Quantum States at Finite Temperature
  An equilibrium state can be represented by a pure quantum state, which we call a thermal pure quantum (TPQ) state. We propose a new TPQ state and a simple method of obtaining it. A single realization of the TPQ state suffices for calculating all statistical-mechanical properties, including correlation functions and genuine thermodynamic variables, of a quantum system at finite temperature. 
Sho Sugiura, Akira Shimizu
cond-mat.stat-mech cond-mat.str-el hep-th quant-ph