Instantaneous Distant Communication via Quantum Entanglement

[IslandPlaya]

I'm afraid you are wrong. You need to transmit information classically to decode the teleported qubits. Its good that there is no need for error correction if what is found is true, but we do not have a means to transmit instantaneously.

[Burninate]

'Reliable quantum communication' may be relevant to communications encryption and perhaps computing, but nobody was seriously predicting any ansible-like FTL comms, and those predictions have not come true.

Still can't beat the speed of light.

[Burninate]

Quantum entanglement does not imply instantaneous communication. This is physics 101.

Physics 103, in fact .

This thread should be merged with http://forum.nasaspaceflight.com/index.php?topic=34854.0

[RonM]

It has no relationship to teleportation of matter (sorry, Scotty will not yet be able to beam you up), however it could allow real time control of Mars rovers or Europa submarines from Earth.

That would be the end of human spaceflight. If you could real time control robots anywhere in the Solar System, there is no reason to send astronauts. Depending on what side of the human exploration vs. robotic exploration argument you are on is whether or not that is a good thing.

[A_M_Swallow]

Application to space.

We cannot transmit information using radio or laser through the sun.  It blocks the beams.  Does the sun block quantum entanglement?

Electromagnetic waves follow an inverse square law.  When the distance doubles the receiver only gets a quarter of the power.  To communicate with say Pluto we need to use very high levels of transmission power, low baud rates, very large dishes and super-cooled antennas.  Information transmission via quantum entanglement may be independent of distance and power levels.  In the future we may get it to work over interstellar distances.

[IslandPlaya]

I'm afraid you are wrong. You need to transmit information classically to decode the teleported qubits. Its good that there is no need for error correction if what is found is true, but we do not have a means to transmit instantaneously.

Thru the sun or not. The same applies.

[JeanPierre_LeRouzic]

Hello,

I will try sum it up in layman terms, apologies if there are any errors:
Indeed not only entanglement is not instantaneous (or FTL) communication, but it is also indirectly subject to attenuation, because in any cases the entangled states, or information that the entanglement is broken, are propagated classically and therefore are subject to attenuation.
Imagine you are on Earth and want to communicate with a satellite, so you send classically an entangled photon to the satellite and keep the other photon near you. As soon the satellite measures the entangled state on its photon, we can measure the same state on our own.

But the "as soon" doesn't mean much.
We can't know when or even if the measurement was done on the satellite by measuring our own photon, as it would destroy the entanglement, so we have to wait to receive the information that the entanglement was destroyed, by classical means. If you can't receive this information because the satellite is too far, or on the other side of the sun, entanglement is useless.
It could be useful for scamgraphy, to create what they call a "shared secret" but there are classical ways to share a secret that do not involve transmission at all.

For example if you had a set of cards instead of a pair of entangled photons, and if you split the set in two without looking at which cards you keep. You send the half set to the satellite, instead of sending a photon. Then at anytime later, without even receiving information from the satellite, if you look at the cards in your half set, you *instantly* know which cards are inside the satellite. You now share a secret with the satellite.

[A_M_Swallow]

Hello,

I will try sum it up in layman terms, apologies if there are any errors:
Indeed not only entanglement is not instantaneous (or FTL) communication, but it is also indirectly subject to attenuation, because in any cases the entangled states, or information that the entanglement is broken, are propagated classically and therefore are subject to attenuation.
Imagine you are on Earth and want to communicate with a satellite, so you send classically an entangled photon to the satellite and keep the other photon near you. As soon the satellite measures the entangled state on its photon, we can measure the same state on our own.

But the "as soon" doesn't mean much.
We can't know when or even if the measurement was done on the satellite by measuring our own photon, as it would destroy the entanglement, so we have to wait to receive the information that the entanglement was destroyed, by classical means. If you can't receive this information because the satellite is too far, or on the other side of the sun, entanglement is useless.
{snip}

How about.  The transmitting equipment could be programmed to send the message at a time T.  The receiver can be programmed to examine its photon at time T+1.  This timing information was given to the transmitting equipment by conventional means, just before rather than after the message was sent.

If we are still limited to the speed of light then the receiver can look at its photon at time T+1+x

where x = distance to satellite / speed of light in the same units.

There is uncertainty about whether a message was sent but two parity bits can detect that 3 out of 4 times.

[savuporo]

Information transmission via quantum entanglement may be independent of distance and power levels.  In the future we may get it to work over interstellar distances.

The phenomenon of quantum entanglement is unable to transmit information - on its own.

"For every qubit teleported, Alice needs to send Bob two classical bits of information."

EDIT: could someone please edit the title of this thread ? It is wrong. There is no "instantaneous communication" or "instantaneous transport of information" happening.

[cordwainer]

I would point out that NIST's JQI experiment merely shows that using daughter beams with a single photon would suffer from too much quantum noise to allow intelligible transmission of information. At much larger scales quantum noise could be overridden to allow for a functionally pure gain signal. Without further experimentation quantum communication cannot be ruled out.

[Burninate]

Yes, much of science fiction is premised on FTL travel and FTL comms.  The actual physics of the thing is rather a lot harder to learn than you might expect, and is deeply nonintuitive (as is general relativity itself)... but please?  Everyone I know who's studied these things mathematically long enough to have some idea what they're talking about says this is physically impossible, and not impossible like 'hasn't been invented yet', but impossible like 'violates the part of our understanding of the fundamental structure of the universe that has withstood most every test we have thrown at it'.  "Instantaneous distant communication" is a trope that is brought up at *literally every media invocation of entanglement*, that the scientists involved in researching it shout down *every single time*, because journalists are trying to misquote them to promise the public FTL.

[TomH]

https://www.washingtonpost.com/technology/2020/07/23/us-plan-quantum-internet/?hpid=hp_national1-8-12_quantum-505pm%3Ahomepage%2Fstory-ans

[ChrisWilson68]

Yeah, it does.

This isn't some technical quandary that will be overcome next week. If faster than light communication becomes possible, it will be new physics, not quantum entanglement.

No:

https://www.washingtonpost.com/technology/2020/07/23/us-plan-quantum-internet/?hpid=hp_national1-8-12_quantum-505pm%3Ahomepage%2Fstory-ans

From the article: A quantum Internet relies on photons exhibiting a quantum state known as entanglement, which allows them to share information over long distances without having a physical connection.

This is not only quantum computing, it also is transmission of information via quantum entanglement.

You misunderstand the article.  When it says "share information over long distances" it means that they are entangled over long distances, so in a sense there is some shared information between them.  It doesn't mean information is transmitted over long distances by the entangled particles.  You'd still have to use normal, slower-than-light-speed, methods to get the entangled particles to the two points separated by a long distance.

It's just like if I wrote an encryption key on carbon paper, kept one copy, and mailed the other copy to someone on the other side of the earth.  The two copies share the information over a long distance in exactly the same sense as the two entangled particles.  I can't use the two copies of the encryption key to do instantaneous distant communication, but I can potentially use them to verify a message sent by normal, slower-than-light-speed communications or to decrypted such information -- just like I could use the entangled particles.

[Twark_Main]

real time control robots anywhere in the Solar System

There's an even deeper problem here: what would "real time" mean exactly? Einstein destroyed the notion of absolute simultaneity. For two events occurring at two spatially separated points, it can be impossible to say which event happened "first" and which happened "second."

Without the notion of absolute time and absolute simultaneity, "instant" communication is worse than impossible, it's nonsensical.

https://en.wikipedia.org/wiki/Ladder_paradox

https://en.wikipedia.org/wiki/Relativity_of_simultaneity

[RSE]

There is a limiting factor in dealing with entanglement communication. All entanglements involve two separate pieces of information – the tangled information and the status of the entanglement. They are not the same, and one can know one piece of information without knowing the other piece. Both are usually thought of as one, bu they are not.

Theoretical example. Schroedinger's paired cats. Two cats are in connected boxes, and they are either alive or dead. Each box is sealed, and they are separated. If one is opened, the entangled information is localized. However, is the status of the entanglement in the other box measured? The answer is actually no.

Here is an experiment one can do to study this point. (And yes, I have done this experiment.)

You will need a laser, a polarized two slit device (each slit at a 90 degree polarization to the other),  a 50/50 beamsplitter, two targets, and two quantum erasers.

Initially shoot the laser through the polarized two slit to a target. You will get two dots. The polarization provides the WYSIWIG information to localize the two beams. So far, strictly Copenhagen.

Now put a quantum eraser in the pathway. I use a rotating polarizer.  At 0 or 90 degrees you will get a dot, either one slit or the other. At 45 degrees, nearly all the light will be blocked, but the small amount that gets through will form a faint interference pattern. The entanglement was restored. (Quantum erasers are now a common feature in non-locality experimentation. Mine is a rawhide method (from Scientific American)).

Now, here's the joker. Place a 50/50 beamsplitter between the two slit and the fist target (removing the quantum eraser.) Point the other paired beam at another target. You will get two sets of dots. (Both have the exactly same WYSIWIG information.) Now for the fun part. Put the quantum eraser back in one path. No matter what you set the eraser at, it won't affect the other target. Put the other quantum eraser in front of the second target. They will act independently of the other. Pathway length (time) does not matter, you can localize before or after the other target. It doesn't matter which target you use, either.

Erasing the WYSIWIG is strictly a local phenomena, it does not propagate to other entangled photons. If it did, you would have an instantaneous communication. Sorry, no “quantum” way out. 

[Twark_Main]

There is a limiting factor in dealing with entanglement communication. All entanglements involve two separate pieces of information – the tangled information and the status of the entanglement. They are not the same, and one can know one piece of information without knowing the other piece. Both are usually thought of as one, bu they are not.

Theoretical example. Schroedinger's paired cats. Two cats are in connected boxes, and they are either alive or dead. Each box is sealed, and they are separated. If one is opened, the entangled information is localized. However, is the status of the entanglement in the other box measured? The answer is actually no.

Here is an experiment one can do to study this point. (And yes, I have done this experiment.)

You will need a laser, a polarized two slit device (each slit at a 90 degree polarization to the other),  a 50/50 beamsplitter, two targets, and two quantum erasers.

Initially shoot the laser through the polarized two slit to a target. You will get two dots. The polarization provides the WYSIWIG information to localize the two beams. So far, strictly Copenhagen.

Now put a quantum eraser in the pathway. I use a rotating polarizer.  At 0 or 90 degrees you will get a dot, either one slit or the other. At 45 degrees, nearly all the light will be blocked, but the small amount that gets through will form a faint interference pattern. The entanglement was restored. (Quantum erasers are now a common feature in non-locality experimentation. Mine is a rawhide method (from Scientific American)).

Now, here's the joker. Place a 50/50 beamsplitter between the two slit and the fist target (removing the quantum eraser.) Point the other paired beam at another target. You will get two sets of dots. (Both have the exactly same WYSIWIG information.) Now for the fun part. Put the quantum eraser back in one path. No matter what you set the eraser at, it won't affect the other target. Put the other quantum eraser in front of the second target. They will act independently of the other. Pathway length (time) does not matter, you can localize before or after the other target. It doesn't matter which target you use, either.

Erasing the WYSIWIG is strictly a local phenomena, it does not propagate to other entangled photons. If it did, you would have an instantaneous communication. Sorry, no “quantum” way out.

At first I thought you were joking with the "quantum eraser" thing, until I looked it up. I had heard descriptions of the experiment itself, but not that specific term. 

https://en.wikipedia.org/wiki/Quantum_eraser_experiment

[zubenelgenubi]

Moderator:
Thread trimmed. Non-sequitur. Does not meet NSF forum discussion standards.

[zubenelgenubi]

Moderator. Same content. Same issue. Again. Trimmed.

Moderator:
Thread trimmed. Non-sequitur. Does not meet NSF forum discussion standards.