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Clovis
- 17
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I would like some help understanding some parts of spontaneous parametric down conversion (SPDC).In the Wikipedia article on the topic…http://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion…the third figure from the top is labeled “An SPDC scheme with the Type II output”. The figure shows two green cones coming out of a crystal. If I understand this figure, the top cone represents the range of possible locations for one of the two down converted photons (let’s say the top cone is the “signal” photon). The bottom cone represents the range of possible locations for the other of the two down converted photons (the “idler” photon). Both cones are shown with circular cross sections at their bottom.Here are my questions:1) In the Wikipedia article, it states that the two photons are “always symmetrically located within the two cones, relative to the pump beam.” Does this mean that if the signal photon is detected at the 12:00 position in the top cone, then the idler photon must be located at the 6:00 position in the bottom cone? And if the signal photon is detected at the 2:00 position in the top cone, then the idler photon must be located at the 8:00 position in the bottom cone?2) If it is true that detection of the signal photon at the 12:00 position in the top cone means that the idler photon must be located at the 6:00 position in the bottom cone, does that mean that the two photons are entangled? My understanding of the term “entangled” is this: Whenever a measurement of a property of one particle determines a property of another particle, the two particles are said to be entangled. It seems to me that the signal photon in the top cone can exist in a range of possible locations before we measure it, but if we measure it to definitely be at the 12:00 position, then we know that the idler photon in the bottom cone is definitely in the 6:00 position. In fact, from my limited understanding of quantum mechanics, I would say that our detecting the signal photon at 12:00 is what caused the idler photon to be located at the 6:00 position. That seems like entanglement to me.The reason I am asking the second question is that the Wikipedia article seems to say that the two photons are only entangled along the lines where the cones intersect. But (as I described above) I feel the two photons are entangled no matter where they are in their respective cones. Am I wrong in that?
Thank you,Clovis
Thank you,Clovis