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From what I understand about the delayed choice quantum eraser is that (per the diagram below), an interference pattern will be seen on D0 if a photon hits the last detectors D1 and D2 where they are scattered by a beam splitter. This observation occurs even if the photon hits the last detectors (D1 and D2) after the other photon hits the interference screen (D0).

From what I can gather here, this means the result of D0 is influenced by D1 and D2 even if D1 and D2 occur after D0.

I can imagine a scenario where D1 and D2 are a large distance away from the pump (maybe 10 light minutes away). If I for whatever reason decide not to put a beam splitter between the detectors, D0 will not show an interference pattern. If this is the case, this means D0 will show the result of whether a beam splitter was placed at D1 and D2 before the photon even hits D1 and D2 (instantaneously).

I could use this to communicate astronomical distances in full duplex by making the decision to put a beam splitter between the detectors as a means to send binary information (interference pattern meaning 0 meaning beam splitter and vice versa). If another person had the same set up but in reverse, they could effectively send information to me instantaneously. If the beam splitter could be toggled on and off very quickly, you could send a stream of video and have a zoom call with someone on Mars.

Furthermore, you could use the mechanism to search for intelligent life anywhere in the universe. All you would do is point it at space and wait for an interference pattern to occur (meaning something was intelligent enough to put your photon stream through a beam splitter). And you would know this information instantaneously, whether that photon would take billions of years to reach its destination, possibly even before that life form even existed.

Furthermore, if I set up a mirror maybe 1 light day away from earth, sent a photon stream towards that mirror which would return, I could instantaneously determine whether a beam splitter was placed in front of the detector in two days. Using this form of information, I could encode something like a video and watch the news that was going to be published in 2 days, so long as I encoded the information with the beam splitter in two days. I could literally see into the future.

What's wrong with my logic?

delayed choice quantum eraser

Alexander Kleinhans
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  • The diagram is obviously from a paper such as this from 1999: https://arxiv.org/pdf/quant-ph/9903047.pdf see figure 2 which has a nearly identical setup. You might guess that this team would have known you would ask this question today if they could see into the future. But they can't. You might have missed the part of the paper where there is a coincidence circuit between the upper and lower arms. That circuit is not omitted in my reference. It features classical communication limited to normal light speed and in the normal direction, to the future. – DrChinese Mar 15 '24 at 23:11

2 Answers2

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Can I use a delayed choice quantum eraser to see into the future?

No.

See for example: What Prevents Delayed Choice Quantum Eraser Experiment from Being Used to Predict the Future?

Vincent Thacker
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Mauricio
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Your logic is rock solid. Axioms? Not so much.

First, you're going to need a laser with a 180,000,000 km coherence length, but let's pretend the applied physics ppl have worked that out.

Now a photon enters the apparatus, it's a bit. Now a blip appears on $D0$--is that blip part of an interference pattern or not? One point does not make a inteference patter. Even in a perfect instrument the node is a point, so the photon for no interference would ever his that point (though you could assign a likelihood to Yes/No interference--could be a good information entropy thing to analyze).

Of course you could modulate that signal at a lower bandwidth than the bit-rate and build up patterns of (non)interference patterns from a few thousand or million photons (with non-zero SNR).

For that, read the article noted in @Maurico's answer. But if you need a 10 minute coherence time, the energy uncertainty of your photon has to be $\Delta E =\hbar/$(ten minutes).

Heisenberg (not the fictional one) says you can't localize that in time to better than $\Delta t= \hbar/\Delta E=10\,$minutes.

JEB
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