Weak-coupling quantum Monte Carlo calculations on the Keldysh contour: Theory and application to the current-voltage characteristics of the Anderson model

We present optimized implementations of the weak-coupling continuous-time Monte Carlo method defined for nonequilibrium problems on the Keldysh contour. We describe and compare two methods of preparing the system before beginning the real-time calculation: the ``interaction quench'' and the ``voltage quench,'' which are found to be suitable for large and small voltage biases, respectively. We also discuss technical optimizations which increase the efficiency of the real-time measurements. The methods allow the accurate simulation of transport through quantum dots over wider interaction ranges and longer times than have heretofore been possible. The current-voltage characteristics of the particle-hole symmetric Anderson-impurity model is presented for interactions U up to ten times the intrinsic level width Γ. We compare the Monte Carlo results to fourth-order perturbation theory, finding that perturbation theory is accurate up to U≈4Γ or for a voltage bias V4Γ. The interplay of voltage and temperature and the Coulomb blockade conductance regime are studied.