Dynamical properties of the spin-boson model using real-time quantum Monte Carlo

We present results for the real-time dynamics of the spin-boson model (a two-state system coupled to a bath of non-interacting harmonic modes) using the inchworm Monte Carlo algorithm. In particular, we study the population difference between the two states at strong system-bath coupling. We focus on sub-Ohmic spectral densities of the bosonic bath, where the system exhibits a second order quantum phase transition between localized and delocalized regimes. The inchworm algorithm is efficient over a wide range of temperatures (including low, intermediate, and high temperatures) and thus allows us to examine the changes in dynamics as the temperature is increased above zero and the emergence of a quantum critical fan.