Quantum eraser experiment
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In
History
The quantum eraser experiment was proposed in 1982 in Marlan Scully and Kai Drühl in the paper Quantum eraser: A proposed photon correlation experiment concerning observation and "delayed choice" in quantum mechanics, as a realizable way to test the hitherto untested predictions of quantum mechanics. As inspirations, the paper mentions Eugene Wigner's focus on the measurement problem, conversations with Willis Lamb, and John Archibald Wheeler's thought experiments. The paper also points out that the experiment could be run in delayed choice mode, as conceptualized by Wheeler's thought experiments, what is now known as a delayed-choice quantum eraser.[4]
The experiment
Concept
This experiment involves an apparatus with two main sections. After two
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.[6] However, the temporal order of measurement actions is not relevant.[7]
Procedure
First, a
Next, a
Finally, a
A double slit with rotating polarizers can also be accounted for by considering the light to be a classical wave.[8] However this experiment uses entangled photons, which are not compatible with classical mechanics.
Other applications
Quantum erasure technology can be used to increase the
Common misconception
A common misunderstanding about this experiment is that it may be used to instantaneously communicate information between two detectors.[10] Simple causation, however, precludes foisting "given" information on the observed outcomes. It is important to understand the role of the coincidence detector in this experimental setup. The linear polarizer in the top path is effectively filtering out half the entangled photons, and via the coincidence detector, is filtering out the corresponding photons in the bottom path. 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. Since there is no way for the detectors to measure whether or not a photon had been part of an entangled pair, that decision is made by looking at the timing, and filtering out any photons that are not picked up at the same time as their 'twin' at the other detector. Thus, when a pair of entangled photons is created, but one of the two is blocked by a polarizer and lost, the remaining photon will be filtered out of the data set as if it was one of the many non-entangled photons. When viewed this way, it is not surprising that making changes to the upper path can have an impact to measurements taken on the lower path, as the two measurements are being compared and used to filter the data.
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. Seeing an interference pattern is only possible by filtering the data with the coincidence detector and only looking at photons that were 1/2 of an entangled pair.
References
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Aharonov, Yakir; Zubairy, M. Suhail (2005). "Time and the Quantum: Erasing the Past and Impacting the Future". Science. 307 (5711): 875–879. S2CID 16606155.
- ISSN 0015-9018.Kastner (2019): 'Delayed Choice Quantum Eraser Neither Erases Nor Delays', Foundations of Physics