Abstract:

In the practice, the non classical feature of the entangled states (of photons in the polarization variable) is observed in the shape of the curve that relates the number of coincidences as a function of the angle between the analyzers. The entangled states are pure states and, in consequence, they are extremely fragile against perturbations. For this reason, it is of practical interest knowing if a curve of coincidences of the same shape can be obtained from a mixed state. The calculation of the form of the most general density matrix that produces the desired correlation curve is carried out in an explicit way. It is concluded that the Bell's states are the only ones that can produce the desired correlation curve. However, if the (non orthodox) hypothesis of probability values outside the range [0,1] is accepted, a family of mixed states is obtained, which is able to produce the desired curve. They have, in addition, some interesting properties, but there is no known method to prepare them