I am currently reading around about squeezed light. I understand as far as the Second-Harmonic Generation (SHG) and Optical Parametric Amplifier (OPA) work, however I do not understand why the signal and idler photons that are produced by the OPA are a squeezed state. All diagrams that I have seen show the pump and seed beams entering the OPA, and then the signal and idler beams leaving, with the label "squeezed". A lot of the literature seems to plainly state that the strong entanglement of the photons (I understand what that is) produces the squeezed state. I do not see that connection myself. If you could please give a physical explanation prior to using any mathematics that would be hugely appreciated. Many thanks in advance!