Full QCD with milder topological freezing

We simulate Nf=2+1 QCD at the physical point combining open and periodic boundary conditions in a parallel tempering framework, following the original proposal by M. Hasenbusch for 2d CP^N-1 models, which has been recently implemented and widely employed in 4d SU (N) pure Yang-Mills theories too. We show that using this algorithm it is possible to achieve an impressive reduction of the auto-correlation time of the topological charge in dynamical fermions simulations both at zero and finite temperature up to two orders of magnitude, allowing to avoid topology freezing down to lattice spacings as fine as a 0. 02 fm. Therefore, this implementation of the Parallel Tempering on Boundary Conditions algorithm has the potential to substantially push forward the investigation of the QCD vacuum properties by means of lattice simulations.