Thermofield theory for finite-temperature many-body physics

Wave function methods are widely used to study ground-state properties of many-electron systems in condensed matter physics and chemistry, and have therefore seen tremendous development over the last fifty years or so. But standard wave function techniques cannot easily be used to compute thermal properties, because doing so requires the entire spectrum and the problem becomes computationally intractable. Thermofield dynamics, which has seen widespread application as a field-theoretical tool to study non-equilibrium properties, provides a wave function representation for the thermal density matrix. In this talk, I will present our recently developed framework (arXiv:1901.06753 and 1907.11286) which shows how the thermofield theory can be utilized to construct finite-temperature generalizations of ground-state wave function methods. I will provide an example of thermal coupled cluster theory and present results for its performance on standard electronic and spin systems.