In delayed-choice quantum eraser experiments, such as those proposed by John Wheeler and performed by Scully and Drühl, the key aspect under investigation is the behavior of quantum particles, particularly photons, in terms of their wave-particle duality and the interference patterns they exhibit.
In these experiments, photons are sent through a series of optical components, including beam splitters and detectors. The experimental setup involves "delayed choices," meaning that the experimenter can choose to measure the path of a photon after it has already passed through the beam splitter.
The intriguing aspect of these experiments is that the measurement choice made after the photon has already passed through the beam splitter can affect the observed interference pattern. If the measurement is designed to obtain information about the path the photon took, the interference pattern is lost, and the particle-like behavior of the photon becomes prominent. Conversely, if the measurement is designed to erase the path information by introducing a specific correlation, the interference pattern re-emerges, and the wave-like behavior becomes dominant.
It's important to note that in these experiments, there is no deletion or alteration of past events, history, or time. The delayed-choice quantum eraser experiments highlight the counterintuitive behavior of quantum particles and their sensitivity to measurement and observation. They demonstrate that the choice of whether to observe or obtain information about the path of a photon can retroactively influence its behavior, seemingly altering the observed outcome.
These experiments challenge our classical intuition by illustrating that the behavior of quantum particles can exhibit both wave-like and particle-like characteristics simultaneously until an observation or measurement collapses the wavefunction, determining the observed outcome. However, the experiments do not suggest that past events or history are deleted or modified in any way. They provide insights into the complex nature of quantum mechanics and the role of observation and measurement in determining the behavior of quantum systems.