Fig. 3
From: Steering is an essential feature of non-locality in quantum theory
Preparation and measurement stages. A UV pump laser at 390 nm was focused onto two β-barium borate (BBO) crystals placed in cross-configuration to produce photon pairs emitted into two spatial modes “a” and “b” through type-I SPDC process. Any spatial, temporal or spectral distinguishability between the photons is removed via a pair of YVO4 crystals, narrow-bandwidth filters (F), and coupling into single-mode fibers (SMF). Then, the photons in each mode are rotated through a half waveplate to get the desired state Eq. (10). For measurement, Alice and Bob uses polarization analyzers consisting of a half waveplate (HWP), a quarter waveplates (QWP), a polarizing beam splitter (PBS) and Di (i = {1, 2, 3, 4}) single-photon avalanche photodiodes
