Entanglement Autodistillation from Particle Decays

Particle decays do not constitute a spin "measurement" in the quantum-mechanical sense but still modify the spin state, in particular, for an entangled system. We show that for a spin-entangled pair of particles the entanglement of the system can increase after the decay of one particle. This unique phenomenon has no equivalent for stable particles and could be observable in top pair production at a high-energy polarized e^{+}e^{-} collider.