Numerical modeling of the central spin problem using the spin coherent   states P-representation
  In this work, we consider decoherence of a central spin by a spin bath. In order to study the non-perturbative decoherence regimes, we develop an efficient mean-field-based method for modeling the spin-bath decoherence, based on the P-representation of the central spin density matrix. The method can be applied to longitudinal and transversal relaxation at different external fields. In particular, by modeling large-size quantum systems (up to 16000 bath spins), we make controlled predictions for the slow long-time decoherence of the central spin. 
K. A. Al-Hassanieh, V. V. Dobrovitski, E. Dagotto, and B. N. Harmon