In a recent paper [Phys. Rev. E 67, 026204 (2003)], Rotter calculates the geometric phases that are picked up by the eigenvectors of a two-state quantum system when an exceptional point is encircled. In addition to the geometric phases observed by Dembowski et al. in a microwave cavity experiment [Phys. Rev. Lett. 86, 787 (2001)], she finds a phase factor of i. We show that Rotters results are inconsistent.
@article{arxiv.nlin/0309066,
title = {Comment on ''Exceptional points and double poles of the S matrix''},
author = {C. Dembowski and B. Dietz and H. -D. Graef and H. L. Harney and A. Heine and W. D. Heiss and A. Richter},
journal= {arXiv preprint arXiv:nlin/0309066},
year = {2007}
}