Decoherence and thermalisation of isolated many-particle quantum states are studied in many different subfields of physics, including high-energy physics. One of the most interesting case are Heavy Ion Collisions which can be holographically connected to string theory in Anti-de Sitter space and for which very detailed data exists. After a general introduction I will focus on the question whether SU(N) gauge theories behave as predicted by the Eigenstate Thermalization Hypothesis (ETH). To answer this question we have performed simulations for low-dimensional SU(2) gauge theories on digital computers (arXiv: 2308.16202) which gave encouraging results. As ETH makes predictions for energy eigenstates the most natural theoretical approach to study e.g. thermalization of QCD is the numnerical simulation of Hamiltonian lattice QCD on quantum computers which, however, is not yet possible. Investigating the validity of ETH on digital computers is an early step in this direction.