Figure 3

Implementation of the protocol of Fig. 2 on an optical table. The rotatable polarizer is implemented thanks to the \(EOM ( \theta ) + P ( 0^{\circ} ) + EOM ( \theta )\) combination. A pump laser of 405 nm generates two beams of 810 nm at the exit of the BBO crystal. Two polarizing beam splitters with two avalanche photodiodes at the exit of each one complete the layout. A pair of mirrors deflect the beams so that the entire setup is contained on the table without having to resort to fiber optics