Emergence of diffusive dynamics in an efficiently-solvable quantum lattice model

Thermalization is a common phenomenon in nature, having a characteristic feature of irreversibility due to entropy increase. However, quantum mechanics, the principle for the microscopic world, is reversible. In past few decades, much effort has been devoted to this field in order to reconcile this conflict, and the eigenstate thermalization hypothesis has been proposed as one way to formulate quantum thermalization. In this talk, I will present our recent work on a one-dimension spinless hardcore fermion model with a variable range of interactions. We solve this problem by mapping it into a free fermion case, and we calculate its time evolution with an efficient Monte Carlo sampling algorithm. We observe that although our model is integrable in energy level spacing, the physical observables show certain thermalization behaviors. Furthermore, with increasing temperature, our system shows a crossover from ballistic to diffusive. It is worth mentioning that in our study we can reach a number of lattice sites of hundreds to thousands, much larger than typical numerical studies on quantum dynamics, which allows us to exclude finite-size artifacts.