Bipartite correlations in quantum resonance states

•We derive a diagonal form of a complex scaled reduced density matrix.•We discuss a measure of bipartite correlations in resonance states.•Model systems of two bosons are considered.

We discuss a diagonal representation of a reduced density matrix determined within the framework of the complex scaling method. We also discuss a possible measure of bipartite correlations in quantum resonance states. As an example, we consider a one-dimensional system of two bosons with a contact interaction subjected to an open potential well. The correlation properties of the lowest-energy resonance state of the system are explored over a wide range of the inter-boson interaction strength, including the Tonks–Girardeau regime.