Experimental demonstration of three mutually orthogonal polarization states of entangled photons

Linearly polarized classical light can be expressed in a vertical and a hor izontal component. Geometrically rotating vertically polarized light by 90 degrees will convert it to the orthogonal horizontal polarization. We have experimentally generated a two-photon state of light which evolves into an orthogonal state upon geometrical rotation by 60 degrees. Rotating this sta te by an additional 60 degrees will yield a state which is mutually orthogo nal to the first two states. Generalizing this procedure, one can generate N + 1 mutually orthogonal N-photon states that cyclicly evolve from one to another upon a geometric rotation by 180/(N + 1) degrees.