Determination of quantum critical point for superfluid-insulator transition in the disordered two-dimensional Bose-Hubbard model

We study superfluid-insulator transition for the disordered two- dimensional Bose-Hubbard model with quantum Monte Carlo simulations. Critical point for on-site Hubbard interaction strength $U_c$ is determined by finite-size scaling for fixed particle density $\rho=0.5$ and on-site disorder potential amplitude $\Delta=12$. We show that an extremely large number of disorder samples is required for such a calculation, implying that previous calculations based on a small number of disorder samples may not be reliable. At the critical point, we also compute the universal DC conductivity value to be $\sigma_ {\rm DC}=0.85\sigma_Q$, where $\sigma_Q=4e^2/h$ is conductivity ``quantum".