Fig. 1: Principle and generation of Thermofield Double state.
From: Variational preparation of finite-temperature states on a quantum computer
a Two identical systems A and B are variationally prepared in an ideally pure, entangled joint state such that tracing out one system yields the Gibbs state on the other. b Corresponding qubits in the two systems are first pairwise entangled to produce the β = 0 TFD state. Next, intra- and inter-system Hamiltonians are applied with optimized variational angles \(\left({{{\boldsymbol{\alpha }}}},{{{\boldsymbol{\gamma }}}}\right)\) to approximate the TFD state corresponding to the desired temperature.
