https://hackerpaper.kaipfister.de/p/1908.05351/Collected HN comments and submissions linking this paper.enMon, 02 Nov 2026 11:16:22 GMThttps://news.ycombinator.com/item?id=20791651urn:hackerpapers:mention:1908.05351:20791651Sun, 25 Aug 2019 06:28:31 GMT<p>&gt; So it was news to me that (a) photons without a common history, and (b) photons indistinguishable in all degrees of freedom could be entangled. Oh no. It is definitely possible to entangle two photons from two different sources. Say two hydrogen atoms emit a photon each; then you just need a non-linear crystal to entangle them, or use linear crystals and post-select good results. Here is a recent example for the latter for quantum repeaters [1], though this has been done for decades now. And making two different photon sources indistinguishable (or controllably-distinguishable) is like the…</p><p><a href="https://hackerpaper.kaipfister.de/p/1908.05351/">Paper and discussion history</a>. A mention is not an endorsement.</p>quant-ph