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Detection of a Quantum Measurement

  1. Apr 25, 2012 #1
    Suppose it is known that a photon has diagonal polarisation (e.g. it has just passed through a diagonal slit), then Alice comes along and measures the photon using a horizontal/vertical polarisation basis. So, I believe there is a 50% chance she will get a horizontal result and 50% chance she will obtain a vertical result.

    Now Bob comes along and also knows the particle has passed through the diagonal slit, but he is unaware that Alice has already made a measurement using a horizontal/vertical basis. Is there an experiment Bob can do to check if the particle's polarisation has been measured?

  2. jcsd
  3. Apr 25, 2012 #2


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    No in this case, and also generally no.
  4. Apr 28, 2012 #3

    Measurement of Alice decreases percentage of Bob's finding diagonal polarized photon to 50%, doesn't it?
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