Superposition, coherence, and $\cal PT$ -symmetry. (arXiv:1802.00480v1 [quant-ph])
In this paper, we investigate $\cal PT$-symmetric quantum mechanics in the
view of superposition and coherence theory. The important connections between
the theories are discussed. It is argued that $\cal PT$-symmetric quantum
systems are endowed with some stationary superposition or superposition-free
property. A physical interpretation of $\eta$-inner product is given, showing
the difference between broken and unbroken $\cal PT$-symmetric quantum systems.