Detecting entanglement of random states with an entanglement witness

The entanglement content of high-dimensional random pure states is almost maximal; nevertheless, we show that, due to the complexity of such states, the detection of their entanglement using witness operators is rather difficult. We discuss the case of unknown random states, and the case of known random states for which we can optimize the entanglement witness. Moreover, we show that coarse graining, modelled by considering mixtures of m random states instead of pure ones, leads to a decay in the entanglement detection probability exponential with m. Our results also allow us to explain the emergence of classicality in coarse grained quantum chaotic dynamics.