Home Discussion Forum If nothing is faster than the speed of light how does photonic...

If nothing is faster than the speed of light how does photonic teleportation through quantum entanglement work?

I am no quantum physics student, just a guy who likes to drink beer while watching the science channel. So, I am not likely to understand an answer that relies on an understanding of the math behind this.
I was watching a show about some of the more ambitious possible inventions of tomorrow hosted by Dr. Kaku, and they were talking about using quantum entanglement to transfer the information between two photons. While the individual photons are not teleported, the information of one is taken on by the other. This quantum entanglement also does not seem to be effected by distance. They did not mention the mechanisms behind quantum entanglement, and I suspect they are not fully understood, but this information has to be transferred somehow. And if distance is not a factor, it seems to me that the mechanism this information is transferred by would be going many, many times faster than the speed of these two photons. Especially if they were to travel in opposite directions. I know my understanding must be flawed, but can someone please point the flaw or flaws out?

4 COMMENTS

  1. well its like this…….
    Euclid is the guy who said that “the shortest distance between two points is a straight line”…..which is observably true and became the basis for Euclidean Geometry.
    NON_Euclidean Geometry states just the opposite….the shortest distance between two points is a curved line. An archer shooting an arrow between mountain tops uses a form of non-euclidean geometry to figure the angle he should hold his bow in relation to the horizon to create the arch necessary to complete the shot.
    Sometimes….in particle physics….a photon can (and regularly does) exist in two different places at the same time…how did it travel from one to the other so quickly as to appear to happen in the same instant? When you fold time and space up so you can put it in your pocket, you will understand. time and space are folded on top of one another and interwoven into each other. When one part of the fold meets another, the tiniest of particles (like photons) can literally be in 2 places at one time.
    There exists more in heaven and earth, Horatio, then are dreampt of in your philosophies……..

  2. You have no real flaws in your understanding. Entanglement _is_ a real phenomenon, but it’s not fully understood. The famous “EPR paradox” from 1935—which deals intimately with entanglement—was originally thought to negate the possibility of quantum mechanics being a complete description of nature (especially as it seems to do an end-run around special relativity), but it seems that relativity is not violated by entanglement. It serves mainly as a good reminder that quantum mechanics can be tremendously counter-intuitive, but not “supernatural”.
    Wikipedia has a pretty good write-up on it ( http://en.wikipedia.org/wiki/Spooky_action_at_a_distance ), but my favorite treatment is probably the book “The Quantum Challenge” ( http://www.amazon.com/Quantum-Challenge-Second-Foundations-Mechanics/dp/076372470X ), which goes into the experimental details, but is rather light on the mathematics (though it does assume a lot from the reader).

  3. For reasons that are fairly complex, it turns out that while you can teleport the *state* of one photon to another, in doing so you don’t actually transmit any *information* between the two. I know this sounds weird, but it’s true. The reason has to do with the fact that a quantum system can have a precisely determined state, while not having precisely determined measurable quantities.
    To put it somewhat vaguely, if you “teleport” a photon state, and then take a measurement from the teleported state, your result is basically impossible to interpret until you know what happens when you measure the other photon, too. The only way to get access to that information is to wait for it to reach you in a conventional manner — i.e., at the speed of light. There’s an example floating around that you can probably find that describes astronauts working on the moon using a quantum system to teleport states back to Earth at faster-than-light speed, but the scientists back on Earth can’t accurately read message encoded in those states until the astronauts also transmit via radio the result of their quantum observations. I recall it being a good example, if you’re able to find it.
    Basically, despite all the quantum weirdness we’ve discovered, as far as we know, it’s still impossible for information to travel faster than light.

  4. The process of quantum teleportation is not faster than light. Let me give you a quick and dirty explanation of the process. You start with three particles, A,B, and C. Particle A is in location X and has a state that you want to have at location Y, but, for whatever reason, you do not want to simply move the particle. What do you do? You teleport it. The first step in teleportation is to put particle B and particle C in an entangled state, so that their states are interrelated (correlated). This process of entangling MUST be done locally, so B and C MUST be next to each other at the beginning. However, the entangling can be done far in advance of the teleportation, so it can be done even before you know what you want to teleport. Then, once B and C are entangled, you send B to location X and C to location Y. Now you have A and B in location X and C in location Y, with B and C being entangled, and you can begin the actual teleportation. To do that, you perform what is called a Bell measurement on particles A and B, together. A Bell measurement will imprint the state of particle A onto the state of particle B, and, at the same time, because B and C are entangled, it will imprint it onto C as well, instantly (sort of faster than light). However, it will imprint it in one of SEVERAL possible ways. That means that though the state of particle C is now related to the state of A, it is related in an unknown way. There is no way to get the state of A out of particle C, since you do not know how they are related! So the imprint was instantaneous, but no information was passed, since there is no way to get that information out of C, at this point.
    However, the Bell measurement does two things. It imprints that information and, at the same time, it tells us in which of the several possible ways that information was imprinted. So a person standing at location X will know how to get the information of desired state out of particle C as soon as the Bell measurement is performed. But a person at Y will not know how to do that, because they will not know the outcome of the measurement. So the person at X must send that information to the person at Y. The process of sending that information can only occur via a classical channel (a telephone, a fiber optic, the internet, a radio broadcast, a post card, etc), and it must occur no faster than the speed of light. Once that information arrives at location Y, the person at Y can then extract the intended state from particle C, and the teleportation is complete. So quantum teleportation is said to require two channels, a quantum channel (the entanglement of B and C) AND a classical channel (the telephone line). The quantum channel is, to some extent faster than light (the the process of establishing the quantum channel… the entangling of B and C and then moving them to X and Y… is no faster than light, usuallyy slower). The classical channel is never faster than light. And you need both of them to perform teleportation. So teleportation is never faster than light/
    You might ask, ‘well, if I need to use a phone to do this teleportation, then why not just tell the people at C what the state is I want and skip the whole entangling nonsense.’ That would be a great question. The reason why quantum teleportation is useful is because a quantum state holds much more information than could be efficiently measured and relayed over a classical channel. This is somewhat buried in the realm of quantum mechanics and quantum information theory, but the quick answer is that if you want to move quantum states, you MUST use a quantum channel. Anything else will simply not work. If you want to move things that are not quantum states (classical states), then using quantum teleportation would be silly and pointless and you should just use your phone. You might wonder who would want to move quantum states, and that is also an excellent question that is buried deep in quantum information science. The answer to that is people who want to make quantum computers and people who are deeply worried about the transmission of top-secret information. But for the average person, there really is no application for this work, at this time. Maybe in 50 years it will be useful to the general public. Or maybe not…
    And you should know that quantum teleportation had been performed with more systems than just photons. It has been done with ions, with clouds of atoms, and more.

LEAVE A REPLY

Please enter your comment!
Please enter your name here

Related