Quantum Monte Carlo loop algorithm for the t-J model

We propose a generalization of the quantum Monte Carlo loop algorithm to the t-J model by a mapping to three coupled six-vertex models. The autocorrelation times are reduced by orders of magnitude compared to the conventional local algorithms. The method is completely ergodic and can be formulated directly in continuous time. We introduce improved estimators for simulations with a local sign problem. Some first results of finite-temperature simulations are presented for a t-J chain, a frustrated Heisenberg chain, and t-J ladder models.