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Home assignment

  1. Sep 2, 2008 #1
    This experiment describes some of the failures of classical physics. Details of this experiment can be found in many sources, and it is interesting to work out the explanation and discover some of the joys of Quantum mechanics. The basic apparatus consists
    of a polarizer. When light is passed through the polarizer, it allows some part
    of the light to pass through. A physical way to think of this is to imagine that
    the polarizer is a measurement device. For example an X polarizer measures how
    much of the light is polarized along the X-direction.
    Consider a beam of light travelling along the X direction.
    (a) The beam is passed through a Z polarizer followed by a Y polarizer. Experi-
    mentally the observed result is 0. Or in other words, none of the light passes
    through. Does this make sense classically ? Explain why or why not.
    (b) Now consider the experiment where the original beam is passed first through
    a Z polarizer followed by a polarizer at 45 degrees to the Z polarizer and
    perpendicular to the X direction. The experiment observation is that 25%
    of the initial light is detected after passing through both the filters. Does it
    make sense classically ?
    (c) Now consider the experiment in which the original beam of light is passed
    through the two polarizers above and then through a Y polarizer. The result
    is that 25 % of the initial light passes through once again. Explain the
    contradiction between the first experiment and this experiment in classical
    physics.
    We have already given the quantum mechanical description of this experiment
    in terms of measurement of the polarization of light. In order to explain the
    results, we shall start with some basic ideas. A beam of light polarized along the
    Z direction is denoted by |Z > and that along the Y direction is |Y >. A beam
    of light in the YZ plane at an arbitrary angle θ to the Z direction can be thought
    of as the ket |I > which is given by
    |I >= |Z > cosθ + |Y > sinθ
    Each time the light passes through a polarizer, one of the directions is picked.
    This can be thought of in terms of the projection operator of the correspond-
    ing polarized state. Now, explain each of the experiments above by performing
    quantum mechanical calculations.


    Can u solve it?????????
     
  2. jcsd
  3. Sep 2, 2008 #2
    Forum rules require you to at least make an attempt at a solution.
     
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