Tuning canonical typicality by quantum chaos

One key issue of the foundation of statistical mechanics is the emergence of equilibrium ensembles in isolated and closed quantum systems. Recently, it was predicted that in the thermodynamic ($N \rightarrow \infty$) limit the density matrix emerges for small subsystems from almost all pure states of large quantum many-body systems. This notion of canonical is assumed to originate from the entanglement between subsystem and environment and the resulting intrinsic quantum complexity of the many-body state. We show that quantum chaos plays a crucial role in the emergence of typicality for large but finite quantum systems. We demonstrate that the degree of typicality can be quantitatively controlled and tuned by the degree of quantum chaoticity present in the many-body system.