%0 Journal Article %T Quantum Treatment for Bose-Einstein Condensation in Non-Equilibrium Systems %A H. Flayac %A I. G. Savenko %A M. M£¿tt£¿nen %A T. Ala-Nissila %J Physics %D 2015 %I arXiv %R 10.1103/PhysRevB.92.115117 %X We develop an approach based on stochastic quantum trajectories for an incoherently pumped system of interacting bosons relaxing their energy in a thermal reservoir. Our approach enables the study of the versatile coherence properties of the system. We apply the model to exciton polaritons in a semiconductor microcavity. Our results demonstrate the onset of macroscopic occupation in the lowest-energy mode accompanied by the establishment of both temporal and spatial coherence. We show that temporal coherence exhibits a transition from a thermal to coherent statistics and the spatial coherence reveals off-diagonal long-range order. %U http://arxiv.org/abs/1503.08424v1