Results

When we add the quantum markers, we mostly see a single slit pattern, which is expected. The double slit interference pattern shows itself slightly in the center of the graph, which is also expected of any non ideal experiment. This is a result of imperfect alignment.

When we add the quantum eraser, we see the double slit interference pattern partially return.

Noise and Limitations

Below is the graph of a background noise test of our apparatus carried out with the light source turned off.

There is a pattern of background noise as a function of the position of the PMT. There are two peaks on the graph, (-1.62, 174) to (-1.53, 175) and (-0.407,175) to (-0.369, 179), that we know that someone had the lights on in the room our apparatus was located in. This means having the lights on in the room significantly affects the results of our experiment.

Noise was a significant issue when trying to see signals with all four polarizers at a low slit width. As Malus' law predicts, each additional polarizer decreased the intensity of the light. By the time the light reached the PMT in the data with the quantum eraser, it had passed through three polarizing filters meaning its intensity was reduced significantly. This became an issue at low slit widths because the intensity became too low to see the signal above the background noise. 34 μm was chosen as the slit width for the experiment because the signal could still be seen after passing through the quantum eraser. At 15 μm, the signal was no longer visible because of the background noise, but no intermediate lengths were tested due to time constraints.

A width of 15 μm produced a double slit pattern with a visibility close to 1 without the markers or eraser, so the width of 34 μm is likely what caused the visibility without the markers or eraser to be less than 1.