Understand
After quantum quenches in many-body systems, finite subsystems evolve non-trivially in time, eventually approaching a stationary state.
- In typical situations, the reduced density matrix of a given subsystem begins and ends this endeavour as a low-entangled vector in the space of operators.
- This means that if its operator space entanglement initially grows (which is generically the case), it must eventually decrease, describing a barrier-shaped curve.
- Understanding the shape of this "entanglement barrier" is interesting for three main reasons: (i) it quantifies the dynamics of entanglement in the (open) subsystem; (ii) it gives information on the approximability of the reduced density matrix by means of matrix product operators; (iii) it shows qualitative differences depending on the type of dynamics undergone by the system, signalling quantum chaos.