We all know how classical interference of waves can be produced by the Michaelson interferometer using the beam splitter and the detectors. No other elements needed to produce classical interference of waves. Setups like this one which create quantum entanglement http://arxiv.org/abs/1212.6136 use beam splitter and detectors, but also use polarizers, wave plates, phase shifters and other elements together to entangle previously separable states. Well, I am not an expert in quantum physics, only in classical physics, so I do not understand the difference between quantum entanglement and classical interference and what is the role that other elements play in the entanglement setup. Could you explain to me what role do these other elements have? Why isn't the basic Michaelson interferometer used instead? What is the role of each element?