If you enjoyed doing these little "quantum" experiments, here are a few others that you might find interesting. If you want to really play the role of a quantum physicist, we recommend that you first try to think about what you expect the results to be, before you actually do the measurements. Then, if the results match your expectations, you will know that you have properly understood the situation; and if the results don't match, you have the opportunity to really learn something! (There's nothing a scientist likes better than to see a surprising result.)

  1. With the initial laser polarization still at 45 degrees, modify the double-polarizer path labeler by replacing one of the halves with a diagonally oriented polarizer, e.g., so the right half is horizontal and the left half is diagonal. What do you think you will observe on the screen?
  2. Now rotate the laser (or the pre-labeler polarizer, if you have one) so that the light intensity after both the horizontal and the diagonal labeler polarizers is about the same. When this is the case, the initial polarization will be at about 22.5 degrees from horizontal. How should the final analyzing polarizer be oriented so that you see perfect fringes (is this even possible)? How should it be oriented so that no fringes at all are observable, i.e., there is complete path information, at least for the photons which are transmitted by the polarizer?
  3. If you happen to have a laser that is emitting mostly unpolarized light, repeat all the steps of the original experiment, but without the preparation polarizer at 45 degrees. Which results will change and which will stay the same?

More to Explore:

View the slideshow of quantum erasure in action

Discuss the experiment in the blog

What You Will Need For the Experiment

What Polarizers Do To Photons

How A Quantum Eraser Works

Notes on Polarizing Film

Troubleshooting the Experiment

More Experiments

Answer to the 3-Polarizer Puzzle Featured in the Print Edition

Whither Waves? More About Interference

Cutting-Edge Experiments: Interfering Soccer Balls

Delayed-Choice Experiments

What Do the Quantum Particles Really Do?

What is Being Erased?