While quantum mechanics underpins particle physics, truly quantum effects are surprisingly difficult to establish in high-energy interactions. A rare exception comes from recent observations of quantum entanglement in top–antitop quark pairs by the ATLAS and CMS experiments. In certain regions of phase space, these particles appear to lie outside the causality cone, making the result even more intriguing. In this talk, I will review the details of these groundbreaking measurements, their implications, and potential criticisms. Additionally, I will explore an exciting possibility: the discoveryof toponium, a bound state of top and antitop quarks. If confirmed, this would be the heaviest known particle, with a mass of 343 GeV—surpassing even the heaviest nucleus, Oganesson, at 279 GeV.