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No teleportation theorem

  1. Oct 4, 2012 #1
    Wikipedia simply says that it is impossible to transform a quantum state to classical info and then back to the same state but doesn't really give a reason why. Can anybody explain in simple terms the reasoning behind this.
  2. jcsd
  3. Oct 4, 2012 #2
    When you measure a quantum state it collapses to one of sometimes many values for that observable. You cannot reconstruct the original state because information has been lost.
  4. Oct 5, 2012 #3
    It's the first step that fails. An arbitrary quantum state of one qubit can be written a|0> + b|1>, where a and b are two complex constants. Because they're continuous they can have any value, and thus be said to represent an infinite number of bits of information. However, any measurement on the system, can only yield either 0 or 1, i.e. one single bit of information. Since an infinite number of bits can never be represented by one single bit, it's of course then clear that you can never copy an arbitrary quantum state to classical information if you only have a single copy of the quantum state to measure on.
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