Conclusion

Conclusion

The visibilities were calculated to be (1.60±0.02)×10^-1 without the markers or eraser, (4.06±0.06)×10^-2 with the marker, and (1.38±0.02)×10^-1 with the marker and eraser.

To correct for an initial visibility lower than 1, the second two values were divided by the first to find out the relative destruction and restoration of the interference pattern.

The quantum markers reduced the visibility of the interference to (25.4±0.4)%.

The quantum eraser then restored the visibility to (86.3±1.3)%.

These values are significantly off from the expected values of 0% and 100%, but we can see that the expected effects are observed to some degree.

The quantum markers destroy most of the interference and the quantum eraser restores most of it.

These imperfect values could be a result of a number of factors.

The quantum markers used were film polarizers which were taped to the double slit with electrical tape. Because of this, the positioning was likely not perfectly orthogonal and could be off by as much as a degree or two. Likewise, the initial and final polarizers were optimized by looking at the intensity of light as a function of the polarization angle with each marker, so they also could be off by a degree or two. If the polarization angle of one of the markers was slightly misaligned, it would prevent the interference from being completely destroyed by the quantum markers, which is likely what happened. Misalignment of any of the four polarizers could also prevent the interference from being completely restored.

Additionally, if the single slit was not perfectly aligned on the center of the double slit, the intensity of the light reaching each of the slits could differ, leading to a lower visibility. This is less likely because the position of the single slit was optimized by placing it on a translation stage and looking for the position that caused the PMT to give the maximum intensity reading.

The incomplete destruction and restoration of interference could also be occurring because the light source used was not completely coherent. The value of dw/λ is 3.11 cm which is beginning to approach the distance the light travels between the single and double slits is 47.5±0.1 cm. The coherence condition is still satisfied, but only by a single order of magnitude.

The frequency range of the bandpass was Δν=1.00×10¹³ Hz, which gives a coherence length of L_c=29.8 μm. Thus the light is not temporally coherent when it reaches the double slit.

In the future, the initial visibility could be raised by using a light source with a longer coherence length and higher intensity such as a laser, reducing sources of noise by light-proofing the black box better or cooling the PMT, and further optimizing the alignment of the polarizers.