Noncyclic Pancharatnam phase for mixed state SU(2) evolution in neutron   polarimetry
  We have measured the Pancharatnam relative phase for spin-1/2 states. In a neutron polarimetry experiment the minima and maxima of intensity modulations, giving the Pancharatnam phase, were determined. We have also considered general SU(2) evolution for mixed states. The results are in good agreement with theory. 
J. Klepp, S. Sponar, Y. Hasegawa, E. Jericha and G. Badurek