Quantum eraser experiment

As inspirations, the paper mentions Eugene Wigner's focus on the measurement problem, conversations with Willis Lamb, and John Archibald Wheeler's thought experiments.

[3] A variation of this experiment, delayed-choice quantum eraser, allows the decision whether to measure or destroy the "which path" information to be delayed until after the entangled particle partner (the one going through the slits) has either interfered with itself or not.

[5] In delayed-choice experiments quantum effects can mimic an influence of future actions on past events.

[7] First, a photon is shot through a specialized nonlinear optical device: a beta barium borate (BBO) crystal.

A stepper motor moves the second detector to scan across the target area, producing an intensity map.

The coincidence detector can only function by comparing data from both sensors, making it impossible to use this setup for instant communication.

In other words, only a small percentage of the light passing through the BBO crystal is split into entangled pairs.

The vast majority of photons passing through the crystal are not split, and must be removed from the final data set as unwanted noise.

Note that in the final state of this experimental setup, measurements on the lower path always show a smeared out pattern on the raw data.

Figure 1. Crossed polarizations prevent interference fringes
Figure 2. Introduction of polarizer in upper path restores interference fringes below