Direct observation of geometric phases without state evolution.

We present a method to measure the geometric phase defined for three internal states of a photon (polarizations) using a three-beam interferometer. From the interferogram, we can extract the geometric phase related to the three states as the area of a triangle formed by interference fringes. Unlike the conventional methods, our method does not involve the state evolution. Moreover, the phase calibration of the interferometer and the elimination of the dynamical phase are not required. [ABSTRACT FROM AUTHOR]