Enhancing Monte Carlo methods by using a generalized fluctuation theory

According to the recently obtained thermodynamic uncertainty relation, the microcanonical regions with a negative heat capacity can be accessed within a canonical-like description by using a thermostat with a fluctuating inverse temperature. This far-reaching conclusion is used in this Letter for enhancing the potentialities of the well-known Swendsen-Wang cluster algorithm in order to access to the anomalous microcanonical states of the q=10 state Potts model on a square lattice, which exhibits a first-order phase transition in its thermodynamical description.