1. An interferometer system comprising: an optical source configured to generate a first pump pulse and a second pump pulse coherent with each other and shifted in time by a delay; a first interferometer configured to receive the first pump pulse and generate an antisymmetric state with two coalescent photons (1/ √{square root over (2)}(|2 1 ,0 2 −| 0 1 ,2 2 )); and a second interferometer configured to receive the second pump pulse and to generate a symmetric state with two coalescent photons(1/ √{square root over (2)}·(|2 1 ,0 2 +| 0 1 ,2 2 )) ; said interferometer system being configured to control the probabilities with which two coalescent photons are emitted from a first output or a second output of the second interferometer; wherein the first and second interferometers are connected so that the interferometer system is configured to output a final state equal to a weighted sum of the antisymmetric state and the symmetric state (1/√{square root over (2)}·(|2 1 ,0 2 +|0 1 ,2 2 )+e iτ· 1/√{square root over (2)}, ·(|2 1 ,0 2 −|0 1 ,2 2 )), the weights of the sum being a function of the delay, wherein the first and second interferometers define a first optical path and a second optical path; and wherein the second interferometer comprises a first crystal of the optically non-linear type and configured to receive the second pump pulse, and first and second optical beam splitters, the first and second optical paths extending between the first crystal and the second optical beam splitter, the first optical beam splitter being interposed between the first crystal and the second optical beam splitter, and being crossed by the first and second optical paths.