Trying to make a quantum eraser at the LTC

Published on: Wed Mar 16 2011

Today’s visit to the LTC began with reading various web pages about Quantum Eraser experiments. To help understand the quantum eraser experiment I watched a few videos about the famous “Young’s Double Slit” experiment. The videos demonstrated how an observer influences the pattern created by photons (or electrons) sent through two slits. When the slit choice of the photons is unobserved they create a double slit interference pattern, but when observed the photons create two bars. The quantum eraser experiment relies on the same idea of observing which way photons in two interfering laser beams are traveling (by measuring the polarization of the two laser beams).

I decided to try out a simple experiment in a Scientific America article about a DIY quantum eraser experiment, and thought I would improve it by using a fine strand to create the diffraction pattern instead of the suggested piece of wire. This turned out to be unwise, because despite creating a very nice diffraction pattern the initial spacing was so fine I was unable to complete the second part of the experiment, which is to polarize the two halves of the “split beam” in orthogonal directions. I left this project alone, but I think I could get it to work next time by using a lens to increase the size of my laser dot, a wire to split the beam and creating a spliced polarizer, ½ horizontal and ½ vertical. If this is placed directly after the wire the interference pattern should disappear and then reappear if I place another polarizer into the beam after the initial polarization.

I continued to try out this idea using the large interferometer, which has an interference pattern. I placed a horizontal polarizer in one beam and a vertical polarizer in the other. The interference pattern disappeared, because the two beams where no longer interacting with each other, but a reduced intensity light still shone through. Rotating a polarizer in this light just reduced the overall intensity. I do not recall if it completely darkened the light at any point and I forgot to record it. I’ll have to check again.