# Homework Help: Home assignment

1. Sep 2, 2008

### isudipta

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. Sep 2, 2008

### Topher925

Forum rules require you to at least make an attempt at a solution.