Temperature-enhanced critical quantum metrology

We show that the performance of critical quantum metrology protocols, counterintuitively, can be enhanced by finite temperature. We consider a toy-model squeezing Hamiltonian, the Lipkin-Meshkov-Glick model, and the paradigmatic Ising model. We show that the temperature enhancement of the quantum Fisher information can be achieved by adiabatic preparation of the state close to the critical point and by preparing it directly in the proximity of the critical point. We also find a relatively simple, however, nonoptimal measurement capable of harnessing finite temperature to increase the parameter estimation sensitivity. Therefore, we argue that temperature can be considered as a resource in critical quantum metrology.