Cluster Monte Carlo algorithm for the quantum rotor model

We propose a highly efficient ``worm''-like cluster Monte Carlo algorithm for the quantum rotor model in the link-current representation. We explicitly prove detailed balance for the algorithm even in the presence of disorder. For the pure quantum rotor model with μ=0, the algorithm yields high- precision estimates for the critical point Kc=0.33305(5) and the correlation length exponent ν=0.670(3). For the disordered case, μ=1/2±1/2, we find ν=1.15(10).