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Revision as of 20:49, 13 July 2011

Using qubits for superluminal communication

I'm probably missing something here, but it seems to me that you really could use qubits for superluminal communication. The article says:

"If Alice wishes to transmit a "0", she measures (...), collapsing Bob's state (...). To transmit "1", Alice does nothing to her qubit."

But I was thinking, instead of just measuring or not measuring, couldn't Alice measure one qubit to transmit a 0, and measure a different qubit to transmit a 1? It could go something like this: Alice and Bob create a state which is an entanglement of three qubits. Then, after it's created, Alice keeps the first and third qubit. Bob takes the second qubit and goes to some far-off distance. So now:

• Alice has ${\displaystyle |\psi \rangle _{A}}$ and ${\displaystyle |\psi \rangle _{C}}$
• Bob has ${\displaystyle |\psi \rangle _{B}}$

Then, to transmit a zero, Alice performs a measurement on only ${\displaystyle |\psi \rangle _{A}}$, and leaves the other two qubits alone. To transmit a one, Alice performs a measurement on only ${\displaystyle |\psi \rangle _{C}}$. Then, after Alice performs her measurement, Bob measures ${\displaystyle |\psi \rangle _{B}}$. The three-qubit state could be initally set up so that:

• ${\displaystyle |\psi \rangle _{A}}$ has a high probability (greater than .5) of being measured as ${\displaystyle |0\rangle }$
• If ${\displaystyle |\psi \rangle _{A}}$ is measured as measured as ${\displaystyle |0\rangle }$, then, subsequently, ${\displaystyle |\psi \rangle _{B}}$ has a high probability of being measured as ${\displaystyle |0\rangle }$
• ${\displaystyle |\psi \rangle _{C}}$ has a high probability of being measured as ${\displaystyle |1\rangle }$
• If ${\displaystyle |\psi \rangle _{C}}$ is measured as measured as ${\displaystyle |1\rangle }$, then, subsequently, ${\displaystyle |\psi \rangle _{B}}$ has a high probability of being measured as ${\displaystyle |1\rangle }$

There would be a probability of error in the transmission, but this error would be less than .5. One could compensate for that error by using many sets of three qubits to transmit each bit. Or maybe one could compensate with classical error-correcting codes.

Would all of that work? I'm guessing that I've missed something, since I'm not an expert on quantum mechanics. Most of what I know is from taking a one-semester class on quantum computing. --Navigatr85 03:10, 22 August 2007 (UTC)

The example

If Bob creates copies and measures them, wouldn't they all have the same spins on each axis? Conversely, how is Bob measuring one of his copies different from Alice measuring her copy?

Contradiction with No-cloning theorem

The page for no-cloning theorem states "The no cloning theorem does not prevent superluminal communication via quantum entanglement, as cloning is a sufficient condition for such communication, but not a necessary one", yet this page says that it does. Who is correct? J0lt C0la (talk) 22:42, 4 October 2009 (UTC)

A thought experiment – using entanglement

A suggestion for a communication system using quantum entanglement:

A(lice) and B(ob) are measuring corresponding particles from pairs of quantum mechanically entangled photons - so-called Bell-couples.

The distance between the transmitter and the source are suitably much shorter than between the source and the receiver, so with synchronized watches the transmitter will detect its twin particle before the other twin reaches the receiver. The transmitter can change its measuring setup by inserting a mirror or not – choice situation, T (1) or T (0). It keeps its choice for an agreed period – for instance 1 / 300.000 sec. The receiver has a fixed preset setup. It should by measuring its part of the pairs with at least 99% probability, guess the Transmitters choice.

As the exchange between the entangled particles takes place instantaneous it will for a growing distance between A and B create superluminal communication.

A suggestion for transmitter and receiver - gives problems UChr (talk) 18:55, 5 June 2011 (UTC)

It occurs to me that in the example method provided allows the direct transfer of information at superluminal speeds. However, the separation of the entangled pair itself cannot occur at superluminal speeds (pending results allowing the acheivement of FTL, which would render the need moot anyways). Thus, if one takes into account the amount of time needed to establish the communication channel, that being the time to separate the particles, can it be reworked to show that it would still be capable of making up the lost time? Ahroun (talk) 19:31, 27 May 2011 (UTC)

I do not fully understand your question so I answer a little widely: Exchange itself / 'communication' between two entangled photons assumed by most to be almost immediate / very much faster than the speed of light. In my proposal takes the transmission of one bit - a 0 or a 1 - 1 / 300000 sec. The separation between A and B should therefore be longer than 1 km - 2 km, for example - to send a bit of information at this way. The source should be located approximately in the middle - ie by around 1 km to both A and B - a little longer when you have to receive - but the route can then be extended by inserting some mirrors. The source should start to produce entangled pairs of photons in advance so they arrive at A and B continuous at the appointed time when A wants to send a bit of information to B. If you want to send for example 100 000 km - it would probably take years to get placed source, receiver and transmitter and test it. A practical application - if it works - is a part in the future. The basic ideas can be tested in a lab. UChr (talk) 16:32, 1 June 2011 (UTC)

Dispute with anon over references

This is getting a bit ridiculous anon188. Most of your challenges to the references are irrelevant or misplaced. In the last edit summary you gave the following as reasons: "Pop science webpage with no content, non-peer reviewed document. Extraordinary claims (sending information back in time), advertising, conflict of interest." Let me address them, though not in the same order:

• Extraordinary claims - no, no extraordinary claims are being made. The claim in the contested sentence is that Cramer is pursuing research on this question. No claim is being made whether or he will be successful nor why or why not. No claims about extraordinary physics is being made - that would require a reliable source of the highest quality. But this again is a claim about what research Cramer, a noted and mainstream physicist, is pursuing. Thus the newspaper article is a valid RS for this very ordinary claim
• Pop science webpage - no, it is a mainstream newspaper article, a valid WP:RS. See WP:NEWSORG.
• non-peer reviewed document - it probably did go through some editorial oversight so it's not just a crank posting on the web, but again, the contested edit is not making a scientific claim, just a claim that Cramer is doing research along these lines
• advertising - I fell to see how the edit and ref run afoul of WP:NOTADVERTISING nor WP:RS. Perhaps though I'm missing your argument. Where do you see the reference with respect to advertising going against WP policies?
• conflict of interest - don't see how the edit or the reference violate WP:COI. I've no connection with Cramer or his work and research.

Additionally, I would argue that information from Cramer's own webpage on the UW servers as well as the CENPA internal report are valid sources for stating what kind of research Cramer is doing. I don't see this as violating WP:SPS. If instead we were using these sources to support the claim new physics and real superluminal communication, then there would be problem. But again, that's not the claim being made, just that a notable physicist is pursuing legitimate research in the subject. The situation is vastly different from extraordinary claims and self-published references you were pushing on Faster-than-light and elsewhere. --FyzixFighter (talk) 17:11, 12 July 2011 (UTC)

Additionally - two points. First, the ref in question has nothing to do with the sentence: "As the quantum eraser experiments rely on a classical, subluminal channel for coincidence detection, it is unclear whether superluminal communication would be possible by this method." So why do you keep removing it with your reverts? Second, if you (anon188) are the same as the other anon user (92.20.54.53) and User:FyzixFighter2, you should probably change that last username via WP:CHU based on WP:IMPERSONATOR. --FyzixFighter (talk) 19:17, 12 July 2011 (UTC)

"FyzixFighter" does not take heed to his/her own standards of the need for properly peer reviewed material. This doesn't include internal university reports (which often have no context, background, citations, survey too) or pop science newspaper items. He or she is looking mentally unhinged and seem to have some connection to the University of Washington or the research and thus this is a conflict of interest. A history of "FyzixFighter" shows this behaviour and numerous cautions/reprimands and a formal complaint will be made. Their actions are compromising the peaceful collective of Misplaced Pages and amount to trolling. People in numerous countries have noticed such on this article and others.