Did you read the whole article you cite? The devil is in the word "ideal". If you actually read that wikipedia article: "a true single-photon source was not cre

Did you read the whole article you cite? The devil is in the word "ideal". If you actually read that wikipedia article: "a true single-photon source was not created in isolation until 1974." and "Another single-photon source came in 1977" and in the 1980's "thus acting as a single emitter of multiple single photons as in the experiments of Diedrich and Walther" and in the 21st century "nitrogen vacancy (NV) centers in diamond have also been utilised as a source of single photons." and "quantum dots (QDs) can emit single photons and can be constructed from the same semiconductor materials as the light-confining structures." The definition of an _ideal_ source is "that it should be on-demand, efficient, robust and easy to implement." It seems fragile, inefficient and difficult to implement sources have been invented multiple times.