  We study the out-of-equilibrium dynamics in the quantum Ising model with
power-law interactions and positional disorder. For arbitrary dimension $d$ and
interaction range $\alpha \geq d$ we analytically find a stretched exponential
decay of the global magnetization and ensemble-averaged single-spin purity with
a stretch-power $\beta = d/\alpha$ in the thermodynamic limit. Numerically, we
confirm that glassy behavior persists for finite system sizes and sufficiently
strong disorder. We identify dephasing between disordered coherent pairs as the
main mechanism leading to a relaxation of global magnetization, whereas genuine
many-body interactions lead to a loss of single-spin purity which signifies the
build-up of entanglement. The emergence of glassy dynamics in the quantum Ising
model extends prior findings in classical and open quantum systems, where the
stretched exponential law is explained by a scale-invariant distribution of
time scales, to both integrable and non-integrable quantum systems.
