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quote:Originally posted by Dr. PraetoriaDoestn't it seem that when dealing with nonlocality and particles, one is at the subatomic level and such particles indicate a "tendency" for not occurring with certanity--at a definite time or ways, but instantaneously?
quote:Originally posted by McQueenI was browsing the web when I came across this article on “Quantum Encryption” published by New Scientist :http://www.newscientist.com/article.ns?id=dn4914 (P.s If you see an empty space at the head of the page , scroll down. ) Can anyone tell me what is happening ? Here is my take on things. Two quantum entangled photons are made through a process known as “parametric down conversion”. Since the photons are “entangled” they posses identical but opposite polarization. One of the photons is sent to a different location (B) , where its polarization is detected , the photon which remained at (A) must now have the opposite polarization. If the photon sent to (B) is interfered with , then the polarization of the photon at (A) will no longer correspond and it is immediately apparent that someone has tried to interfere with the transfer. But what does this achieve ? If the time and duration of the transfer is known together with the intervals at which the photons are sent , then even a child could break the encryption . So why not just use morse code instead , the only advantage is that with entangled photons , one would be aware of any attempts to interfere with the transfer process. Am I right in thinking this , or have I missed something. Further what does it prove about non-locality ?
quote:Originally posted by gsmollin
quote:The entangled photons are used only to transmit a cryptographic key to two separated locations. The value of the key is random, but it is known in two separated locations, and the transmission of the key was secure. Now this key is used in one location to encrypt a message. Then the message is sent conventionally to the other location, where the key is used to decrypt the message. This key is used only once. A new key is transmitted by entangled photons for the following message.
quote:Originally posted by gsmollinThe entangled photons are oppositely polarized as they separate. Of course we are using mixed metaphors when we say that. The direction of spin is the proper term for a photon. Polarization is the matching property of the photon's wave function.I cannot answer your question, however. As far as I understand the process, querying the spin of the photon requires its destruction. How this affects the entangled photon is unclear. It should result in a matching destruction if spin is to be conserved, but how would the matching photon be read at the other location if that happened? This is intriguing, and I would like to study the details, assuming they are public.
quote:So the photon splits at the mirror,...