  We resolve the real-time dynamics of a purely dissipative $s = 1/2$ quantum
spin or, equivalently, hard-core boson model on a hypercubic $d$-dimensional
lattice. The considered quantum dissipative process drives the system to a
totally symmetric macroscopic superposition in each of the $S^3$ sectors.
Different characteristic time scales are identified for the dynamics and we
determine their finite-size scaling. We introduce the concept of cumulative
entanglement distribution to quantify multiparticle entanglement and show that
the considered protocol serves as an efficient method to prepare a
macroscopically entangled Bose-Einstein condensate.
