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Day 2.7
Quantum Polarization and Entanglement
1) You are wearing a pair of 3-D glasses. How much light gets through?
A) exactly 50% because of symmetry
B) exactly 50% because cos2 (45o) = ½
C) around 50% because the filters are not perfect
D) around 50% because of human error
Explain:
2) Suppose a single, vertically polarized photon is heading toward the filter in front of your right eye. The
filters in the glasses are at 45o to vertical. What will get through the filter?
A) half a photon
B) a photon with half the energy
C) a photon
D) no photon
Explain: How does this illustrate quantum uncertainty?
3) Suppose 100 vertically polarized photons are heading toward the filter in front of your right eye. What
will get through the filter?
A) exactly 50 photons
B) at least 50 photons
C) around 50 photons
Explain: How does this illustrate intrinsic randomness?
4) Suppose a vertically polarized photon is heading toward a filter at 45o and then toward a horizontally
polarized filter. What is the chance that a photon will make it through both filters?
A) 25%
B) 12.5 %
C) 6.25%
D) 0%
Explain: How does this demonstrate measurement-disturbance?
5) How do these various thought experiments illustrate wave-particle duality?
Next we will explore what happens when you put polarization and interference together.
6) Light passes through two slits that are close together and then hits a screen. What will you see?
A)
B)
C)
Explain:
7) Light heads toward two slits that will normally produce the pattern shown in answer A) above. However,
one slit is covered by a vertical polarizer and the other by a horizontal polarizer. What will you see now?
A)
B)
C)
Explain:
8) The set up is the same as the last question. In addition, a third polarizer is placed in between the slits and
the screen. What will you see?
A)
B)
C) it depends on_______
Explain:
9) Suppose that the third filter was at 45o and the experiment was done with only one photon at a time. If the
image was allowed to build up slowly over time you would see
A)
B)
C)
Explain:
10) Polarization can be explained by classical waves and by quantum physics. Which is most fundamental?
A) Quantum
B) Classical Waves
C) Neither
D) Both
Explain:
Certain crystals can take one photon and produce two photons with half the energy. These photon pairs are
said to be entangled because they have identical - but still random - polarization. If you measure the
polarization of one of them, you immediately know the polarization of its partner.
11) Modelling Entanglement with concrete objects;
a) Explain how entangled gloves work.
b) Explain how entangled coins work.
12) One of a pair of entangled photons is sent toward double slits that normally produce an interference
pattern. These slits are covered with horizontal and vertical polarizing filters. The partner photon is sent off
in a completely different direction - it never goes near the slits. This is repeated many times and the number
of photons (vertical) vs. detector location is graphed.
a) Which of the following graphs shows what you will get if you graph the number of photons (vertical) vs.
detector location?
A)
B)
C)
Explain:
b) The experiment is repeated, but now the photon that does not go near the slits is sent thorough a third
polarizing filter which is at 45o to vertical. Which of the above graphs shows what you will get? Explain:
c) The experiment is repeated, but we only keep the data for photons whose partners made it through the
filter. Which of the above graphs shows what you will get? Explain:
13) Entanglement is a key aspect of quantum computing. To get a sense of how these are different from
classical computers go to Quantum Tic-Tac-Toe. http://countergram.com/qtic/
a) How is it quantum Tic-Tac-Toe different from the regular game?
b) How does it demonstrate the key concepts of quantum physics, including entanglement?