Tripartite separability of four-qubit W and Dicke mixed state in noise environment Li-li Ge, Miao Xu, Tao Hu, Li-zhen Jiang and Xiao-yu Chen Eur. Phys. J. Plus, 136 7 (2021) 739 Published online: 10 July 2021 DOI: 10.1140/epjp/s13360-021-01729-w