Introduction

Introduction

Ever since Thomas Young’s famous double slit experiment in 1801, physicists have been trying to gain a better understanding of the behavior of light. The double slit experiment shows that light sent through double slits constructively and destructively interferes, behaving as a wave would. This experiment explores a natural expansion of Young’s double slit experiment into the realm of quantum mechanics using polarizers.

In this experiment, each of the slits is covered by a polarizing filter. The two filters are mutually orthogonal, meaning that the polarization components of the light from each slit cannot interfere, erasing the double slit interference pattern and replacing it with a single slit pattern. This is why the two filters are called quantum markers; they mark each individual photon with information about which slit it traveled through by changing the polarization angle. If a third polarizing filter is placed immediately after the markers with a polarization angle oriented 45 degrees from each marker, the polarization components of the light from each slit are changed again so that they are no longer orthogonal. This erases the information that specified which slit each photon traveled through, hence why this polarizer is called the quantum eraser [1]. Thus double slit interference is restored.

The theory behind this experiment can be described both by quantum mechanics via a superposition of polarization states and classical physics via the wavelike behavior of light and Malus’ law. Our discussion of the theory will focus on the classical physics that motivates this experiment including single slit diffraction, double slit diffraction, and Malus’ law. This site also includes a discussion of the experimental apparatus and methods involved in the experiment, and the results obtained. Finally, the visibility of measured interference patterns are calculated and interpreted in the analysis and conclusion sections.