Non-Markovianity of a qubit coupled with an isotropic Lipkin–Meshkov–Glick bath
Tian Li-Jun, Ti Min-Min, Zhai Xiang-Dong
       
The curves of h ( t ) versus time t with different λ are plotted in panels (a), (b), (c), and (d) for N = 500, λ′ = 0.5.