We show that the geometric phase for mixed state during a cyclic evolution suggested in 2004 J. Phys. A 37 3699 is U(1) invariant and can be observed by nowaday techniques.
@article{arxiv.quant-ph/0407076,
title = {Reply to "comment on Geometric phases for mixed states during cyclic evolutions"},
author = {Li-Bin Fu and Jing-Ling Chen},
journal= {arXiv preprint arXiv:quant-ph/0407076},
year = {2009}
}