The delayed-choice quantum eraser is finally debunked

Aractus 04, November, 2021

By Sabine Hossenfelder:


Didn’t I say this a decade ago? Yes indeed I did, and admittedly I did get some things with my old analysis wrong, but I was 2/3rds of the way there which is a LOT closer than people who were saying “oh yes this experiment proves entanglement has effects going backwards in time”. You can see that in my old explanation what I said was that “They came to this conclusion because it is consistent with the predictions of Quantum Mechanics, but they failed to correctly observe their own results. I said earlier that an entangled pair for the purposes of this experiment can be thought of as being a single particle, right? Well then the ‘signal’ photon tells us whether or not the ‘idler’ photon has an interference pattern. When you look at it like this, the results tell a different story.” And then incorrectly asserted that the interference pattern happens from photos interfering with each other somehow. That’s a little embarrassing.

No I kid you, it isn’t. That part was wrong, but in my defence I had assumed it was indeed a true interference pattern (which it isn’t). If I had access to actually read the scientific paper I’m sure I would have done a better job, but alas that also illustrates the problem with the Academy and access to research.

Okay so let’s now set the record straight and correct my own error from 10 years ago in the process.

delayed choice quantum eraser experiment

So in short, when a particle “goes” through a single slit the quantum mechanics wave function produces a single-slit interference pattern, and as there are two slits they overlap to form a blurry blob on the detection screen. So why don’t you see this pattern when they hit D3 and D4 and only with D1 and D2? That is an excellent question, not addressed by Sabine and really because it ultimately doesn’t matter as if it were a true interference pattern then D1 + D2 would show it, which it doesn’t.

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