Sorry to disturb you again, but I thought of what you said in my previous questions. Dichroic mirrors, polarizers are used in the above entanglement experiment but according to their encyclopedic definition, they only filter light by color and polarization. Half-wave plates and quarter-wave plates rotate the polarization of light. Microwave control lines supply microwaves for rotating the spin of the qubits. Polarizing beam splitters play role in measurement of the light polarization. The only element that seems to create entanglement is the non-polarizing beam splitter together with the detectors. The below article also mentions only beam splitter and detectors in its scheme http://arxiv.org/pdf/1309.2867v2.pdf (a) Schematic of the system for entanglement generation: Two distant quantum dots, QD1 and QD2 , are driven by coherent light resulting in fluorescence which interferes at a beam splitter, BS. The outputs of the beam splitter are detected by two photomultiplier photon number detectors, D1 and D2, which provide postselection of the entangled state. The photon paths are labeled a, b, c and d. Notice how the quantum dots are not sources of entanglement, but rather the objects which are entangled in the experiment. I notice no use of nonlinear crystals, which could mean they are not always necessary. I am not saying all these because I want to start an argument with you, but because I cannot see any role that other elements in the above image play in entanglement. According to their definitions I read on Wikipedia, they are only polarizers, detectors, filters, but not entanglers. Only the beam splitter seems to play this role.