TEPID-ADAPT: Adaptive variational thermal state preparation at low temperatures

Adaptive variational quantum algorithms have found a wide range of applications in physics and chemistry, especially for ground-state preparation. Quantum systems in reality are at finite temperatures, where the state of interest is the Gibbs state of the Hamiltonian. As a result, it is of great importance to develop methods to prepare Gibbs states, particularly at low temperatures. In this work, we propose a new method to prepare the thermal Gibbs state at low temperatures using a variational method that is partially adaptive and uses a minimal number of ancillary qubits.