Consider a particle with a two-level property that can be either | 0 ⟩ ⟩ or | 1 ⟩ ⟩ , this can be for example the horizontal and vertical polarization of a photon or the spin projection of a spin-1/2 particle as in the previous example with the neutrons. One of these two polarization states (let's say | 0 ⟩ ⟩ ) is chosen and the particle is then prepared to be in the following superposition: