Comment on ''Exceptional points and double poles of the S matrix''

Dembowski, C.; Dietz, B.; Graef, H. -D.; Harney, H. L.; Heine, A.; Heiss, W. D.; Richter, A.

Comment on ''Exceptional points and double poles of the S matrix''

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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.