Thermalization is an elusive phenomenon in quantum mechanics. Since according to the AdS/CFT correspondence, a
black hole in the bulk spacetime is dual to a thermal state in the boundary CFT, thermalization in the CFT is dual to
black hole formation in AdS. Thus, understanding quantum thermalization is likely a key component in understanding the
information paradox—the contradiction between QFT and general relativity occurring when a black hole seemingly erases the information of whatever went into creating it.
In this thesis we investigate different aspects of quantum thermalization in simple field theories that have conjectured
holographic duals, or more specifically, free large N singlet models. Since such theories are free and hence integrable,
thermalization is more subtle but nevertheless appears in different forms. We investigate the late-time quench dynamics
of a version of the O(N) vector model with probes such as the effective density matrix and the spectral density function.
We refine an operator thermalization hypothesis and explore its consequences in different spacetime dimensions in general
large N singlet models. We also discuss the prospect of using thermal mixing in the boundary theory as a diagnostic of
strong gravity in the bulk.

Keywords: AdS/CFT, thermalization, quench, large N singlet models, emergent spacetime.