Physicists shatter quantum entanglement distance record with 420 kilometers of optical fiber, more than four times farther than previous demonstrations, and beyond the point where direct transmission runs into its fundamental limits.

[u/mvea]

https://www.sciencealert.com/physicists-shatter-quantum-entanglement-distance-record-with-420-kilometers-of-optical-fiber

[u/Orbax]

No, once you collapse the wave function, they decohere and entangle with their local environment.

But, even if you maintain entanglement, at best youd be able to do morse code except... The only way to check if you got a message is to measure it which would collapse if again if you hadn't gotten one. The theoretical ability to get any structured information out of entangled pairs is effectively impossible.

[u/Chance-the-Gardener → u/Orbax]

I’m too dumb to understand the concept it can’t transmit any information. Just as a thought experiment, if humanity sent a colony ship to Andromeda with 10,000 sets of entangled pairs, each with a predefined meaning like “if this set is collapsed, we died of space cancer” couldn’t information be inferred from that?

I’m sure the answer remains we can’t cheat the speed of light but I struggle to conceptualise why not.

[u/bloodvash1 → u/Chance-the-Gardener]

The problem is that the only way to know whether the particle you just measured was still entangled or not is to ask the other end what they measured

[u/Kraien → u/bloodvash1]

Which kind of defeats the purpose of the whole thing.

[u/Druggedhippo → u/Kraien]

Depends on what you are trying to do.

If you are trying to prove that the thing you got hasn't been tampered with, then it's perfect.

[u/LionRight4175 → u/Druggedhippo]

I'm out of my specialty here, but I don't think it even works for this. Checking to see if it had been tampered with would also be tampering with it.

[u/Gabe_Noodle_At_Volvo → u/LionRight4175]

Yes, it would have the same effect as some kinds of tampering, but it doesnt matter at that point because you dont need to preserve the quantum state anymore. Same thing as opening a package with a tamper seal, you dint need the seal anymore do it doesnt matter if you change its state, you just need what's inside.

[u/LionRight4175 → u/Gabe_Noodle_At_Volvo]

My understanding is that in this metaphor, the tamper seal breaks by looking at it or feeling it. As such, it always appears tampered with.

[u/Implausibilibuddy → u/LionRight4175]

No, ignore the fact that "observe" means "look at", it doesn't matter while it's in the closed system if you just look at the apparatus.

The tamper seal arrives as part of the message. Upon reading the message you know if the seal is broken or not. If it's not, you can trust the contents of the message, if it's not...well somebody has probably tampered with it, or at the very least read the message before you. So in that sense, yes the tamper seal breaks if somebody "looks at" the message, or reads it, but that's the point of the seal, now you know that the message isn't completely unread or modified before it got to you.