Albert Einstein called it "spooky action at a distance". He hated the concept of quantum mechanics, saying "God does not play dice with the Universe". Unfortunately, Einstein was quite wrong. The idea is that pairs of photons can be generated and can go virtually any distance, and then a measurement made on one of these photons essentially instantaneously determines the equivalent value of the other photon. There is apparently no limit to the distance over which this can be done. A few years ago I read that the apparent velocity of this connection is at least 10,000 times c, or the speed of light in a vacuum. [1]https://blogs.scientificamerican.com/news-blog/quantum-weir dnes-wins-again-entangl-2008-08-13/#:~:text=(In%202007%2C%20researchers %20transmitted%20entangled,two%20of%20the%20Canary%20Islands.)&text=But %20in%20reality%2C%20no%20experiment,times%20the%20speed%20of%20light. "The photons were indeed entangled, the group reports in [2]Nature. But in reality, no experiment is perfect, so what they end up with is a lower limit on how fast the entanglement could be traveling: 10,000 times the speed of light." I'm not a good person to be explaining this to you: My degree is in chemistry, not physics. But read up on Bell's inequalities. (different Bell!) [3]https://en.wikipedia.org/wiki/Bell%27s_theorem "Bell's theorem proves that [4]quantum physics is incompatible with [5]local hidden variable theories. It was introduced by physicist [6]John Stewart Bell in a 1964 paper titled "On the [7]Einstein Podolsky Rosen Paradox", referring to a 1935 [8]thought experiment that [9]Albert Einstein, [10]Boris Podolsky and [11]Nathan Rosen used to argue that quantum physics is an "incomplete" theory.^[12][1]^[13][2] By 1935, it was already recognized that the predictions of quantum physics are [14]probabilistic. Einstein, Podolsky and Rosen presented a scenario that, in their view, indicated that quantum particles, like [15]electrons and [16]photons, must carry physical properties or attributes not included in quantum theory, and the uncertainties in quantum theory's predictions are due to ignorance of these properties, later termed "hidden variables". Their scenario involves a pair of widely separated physical objects, prepared in such a way that the [17]quantum state of the pair is [18]entangled. " [partial quote] Quantum communication over fiber optics has been done to a record distance of 50 kilometers. [19]https://www.sciencedaily.com/releases/2019/08/190829150732.htm#:~:t ext=For%20the%20first%20time%2C%20a,for%20a%20future%20quantum%20intern et.&text=FULL%20STORY-,For%20the%20first%20time%2C%20a%20team%20has%20s ent%20a%20light,50%20km%20of%20optical%20fiber. Ironically, I have actually made a major contribution to this field, although almost nobody realizes it yet. The limit to the distance of quantum entanglement, 50 kilometers above, is based on the amount of optical loss present in the fiber. Prior to my invention, and currently, the record for a low-loss single-mode optical fiber is by Sumitomo Electric, and is 0.1419 db/kilometer. [20]https://global-sei.com/company/press/2017/03/prs029.html#:~:text=No w%20Sumitomo%20Electric%20has%20advanced,lowest%20loss%20of%20optical%2 0fiber. Fiber optics scientists and engineers achieved a fiber loss of about 0.200 db/km in 1978, and about 0.160 by the mid-1980's. They are apparently approaching a limit asymptotically, the limit defined by the presence of natural-quantities of spin-containing isotopes in silica. In about December 2008, while stuck in a Federal prison cell at USP Tucson, Arizona, I realized that the cause of the residual loss in these fibers is the Si-29 and O-17 isotope atoms, and for Corning-type fibers (containing germania, or GeO2, dopant), the Ge-73 isotope atoms. Remove these spin-containing isotopes from optical fiber silica, and it should be possible to drop the loss by at least a factor of 100, or to about 0.001db/kilometer. (Corning-type fibers use a core of 8% GeO2 and 92% SiO2, and pure silica in the cladding. Sumitomo-type fibers use(s) a pure-silica core, and a fluorine-doped cladding. Since there are fewer spin-containing isotopes in pure silica than in germania-doped silica, Sumitomo had/has a small loss advantage over Corning.) If this fiber is used for comunication between New York and Ireland, the hop should be achievable by a single, continuous fiber. It will not need to contain the 40-odd EDFA [21]https://en.wikipedia.org/wiki/Optical_amplifier amplifiers currently employed. Similarly, if such fiber is used for a quantum link, it should be possible to do the link at least at a distance of 5000 kilometers, 100x better than the recent (2019) record. The Chinese have been doing entanglement experiments on a satellite named Micius. [22]https://en.wikipedia.org/wiki/Quantum_Experiments_at_Space _Scale "QUESS is a proof-of-concept mission designed to facilitate [23]quantum optics experiments over long distances to allow the development of [24]quantum encryption and [25]quantum teleportation technology.^[26][7] Quantum encryption uses the principle of [27]entanglement to facilitate communication that is totally safe against [28]eavesdropping, let alone [29]decryption, by a third party. By producing pairs of entangled [30]photons, QUESS will allow ground stations separated by many thousands of kilometres to establish secure [31]quantum channels.^[32][3] QUESS itself has limited communication capabilities: it needs [33]line-of-sight, and can only operate when not in sunlight.^[34][8] " Jim Bell On Monday, June 29, 2020, 12:43:08 AM PDT, таракан wrote: I quote the main title of the article: "Scientists in China managed to exchange a crypto key at a distance of over 1,000 kilometers" Wow! How can they do that? On Monday, 29 June 2020 г., 2:54, jim bell wrote: Cointelegraph: Experts Split on Practical Implications of Quantum Cryptography. [35]https://cointelegraph.com/news/experts-split-on-practical-implications-of-qu antum-cryptography References 1. https://blogs.scientificamerican.com/news-blog/quantum-weirdnes-wins-again-entangl-2008-08-13/#:~:text=(In 2007, researchers transmitted entangled,two of the Canary Islands.)&text=But in reality, no experiment,times the speed of light. 2. https://www.nature.com/nature/journal/v454/n7206/edsumm/e080814-10.html 3. https://en.wikipedia.org/wiki/Bell's_theorem 4. https://en.wikipedia.org/wiki/Quantum_physics 5. https://en.wikipedia.org/wiki/Local_hidden_variable_theory 6. https://en.wikipedia.org/wiki/John_Stewart_Bell 7. https://en.wikipedia.org/wiki/EPR_paradox 8. https://en.wikipedia.org/wiki/Thought_experiment 9. https://en.wikipedia.org/wiki/Albert_Einstein 10. https://en.wikipedia.org/wiki/Boris_Podolsky 11. https://en.wikipedia.org/wiki/Nathan_Rosen 12. https://en.wikipedia.org/wiki/Bell's_theorem#cite_note-EPR-1 13. https://en.wikipedia.org/wiki/Bell's_theorem#cite_note-Bell1964-2 14. https://en.wikipedia.org/wiki/Probability 15. https://en.wikipedia.org/wiki/Electron 16. https://en.wikipedia.org/wiki/Photon 17. https://en.wikipedia.org/wiki/Quantum_state 18. https://en.wikipedia.org/wiki/Quantum_entanglement 19. https://www.sciencedaily.com/releases/2019/08/190829150732.htm#:~:text=For the first time, a,for a future quantum internet.&text=FULL STORY-,For the first time, a team has sent a light,50 km of optical fiber. 20. https://global-sei.com/company/press/2017/03/prs029.html#:~:text=Now Sumitomo Electric has advanced,lowest loss of optical fiber. 21. https://en.wikipedia.org/wiki/Optical_amplifier 22. https://en.wikipedia.org/wiki/Quantum_Experiments_at_Space_Scale 23. https://en.wikipedia.org/wiki/Quantum_optics 24. https://en.wikipedia.org/wiki/Quantum_encryption 25. https://en.wikipedia.org/wiki/Quantum_teleportation 26. https://en.wikipedia.org/wiki/Quantum_Experiments_at_Space_Scale#cite_note-Spacecom-7 27. https://en.wikipedia.org/wiki/Quantum_entanglement 28. https://en.wikipedia.org/wiki/Eavesdropping 29. https://en.wikipedia.org/wiki/Cryptanalysis 30. https://en.wikipedia.org/wiki/Photons 31. https://en.wikipedia.org/wiki/Quantum_channel 32. https://en.wikipedia.org/wiki/Quantum_Experiments_at_Space_Scale#cite_note-IOP-3 33. https://en.wikipedia.org/wiki/Line-of-sight_propagation 34. https://en.wikipedia.org/wiki/Quantum_Experiments_at_Space_Scale#cite_note-Xinhua-8 35. https://cointelegraph.com/news/experts-split-on-practical-implications-of-quantum-cryptography