# Quantum typicality: what is it and what can be done with it?

Jochen Gemmer, Osnabrück University

13.06.2014 at 10:15

Two pure quantum states which may be very different according to various definitions may nevertheless exhibit very similar expectation values of certain observables, reduced density matrices for subsystems etc. The fact that this phenomenon is not only possible but in a sense very likely to occur is today known as "quantum typicality". Thus, the concept of quantum typicality has become the starting point of explanations of thermodynamical relaxation in closed quantum systems.

Maybe less known is the fact that the full dynamics of some expectation value may be very similar, even if calculated from almost random initial states. This finding goes by the name of dynamical typicality and may be used to simplify the numerical calculation of dynamics of mixed states, finite temperature correlation functions or extract information concerning the eigenstate thermalization hypothesis.

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