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Sustained, high-fidelity quantum teleportation

news.fnal.gov

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Re: Sustained, high-fidelity quantum teleportation

#101

Post by CreepGin »

edge17 wrote: post #84
pontus wrote: post #75

Earlier quoted context omitted.

The receiver does not know that a message has been sent until the first person contacts them classically. It's a common mistake to think that quantum teleportation is a new way of sending information. It's really a way to use classical communication in order to leverage entanglement to bypass various limitations of quantum mechanics. So, the two people communicating would e.g. start out together and create a pair of…

Got it, thanks for the explanation. Also, not to get ahead of ourselves (understanding this is research), but what is the use/benefit of this method? We can already send and receive information over great distances with and without wires at seemingly high speeds. Is this a new level of speed? Are there some previous limitations of distances that are now surmountable? Is the power or cost envelope required somehow red…

I think you missed his remarks:

> The receiver does not know that a message has been sent until the first person contacts them classically. It's a common mistake to think that quantum teleportation is a new way of sending information. It's really a way to use classical communication in order to leverage entanglement to bypass various limitations of quantum mechanics.

Re: Sustained, high-fidelity quantum teleportation

#102

Post by davidhyde »

pontus wrote: post #75
edge17 wrote: post #51

Earlier quoted context omitted.

Maybe I'm dense, but I still don't understand. The cloning explanation made sense to me, but to the original question - how does the recipient know the message is done being sent without the sender picking up the phone and calling the recipient...? i.e. Is there some equivalent of a termination code/header sort of thing that the recipient is looking for in the 'bit stream' or whatever? Or am I not even thinking about…

The receiver does not know that a message has been sent until the first person contacts them classically. It's a common mistake to think that quantum teleportation is a new way of sending information. It's really a way to use classical communication in order to leverage entanglement to bypass various limitations of quantum mechanics. So, the two people communicating would e.g. start out together and create a pair of…

Thank you for all your comments, very illuminating! Is the following classical analogy flawed? Say you have two pendulums and you set them in motion together so that they swing in perfect synchrony. Then you move the one (still swinging) pendulum to another location without disturbing it. Would it be reasonable to say that the physical pendulums are the “medium” and evolving information about the exact position and velocity of the pendulums the “system”? Because this is a classical system you can measure the position and velocity of the one pendulum and know that the other pendulum is at the exact same position and velocity. They are “coherent” in a way. However, in a quantum system, the medium (say a photon of light) is so fragile that measuring it removes its coherence to its entangled twin. This decoherence does not destroy the photon but the future information it carries. It now carries new information unrelated to the originally entangled photon. Kind of like having to stop a pendulum to figure out it’s position and velocity. You haven’t destroyed the pendulum but you have destroyed the potential for it to give you information about the other pendulum in the future. Following on from this analogy, if you crashed pendulum c into your one pendulum and destructively measured the resulting position and velocity you could send this information to the second pendulum to get that pendulum to set another pendulum in motion that would have an identical future to pendulum c before its system was destroyed. Thus, no information is really flowing between the two entangled photons because they are just “vibrating” identically until one is disturbed.

Re: Sustained, high-fidelity quantum teleportation

#103

Post by Technically »

Rooster61 wrote: post #97

So, something that always bothered me, and my admittedly ignorant understanding of QM as a non-physicist. I understand that the quantum state of a particle can be teleported, and that classical information must be passed to observe the particle and collapse the state correctly. My question is, if we can't observe the particle, how do we know that that particle is entangled with the original one?

The particle can observed, but this collapses the entanglement. If the key derived from entangled particles is bad, and communication does not work with the observed key, you know with high probability the particle collapsed pre-entanglement, and and you resync to agree on a new key. There is no way to tell without comparing (classical) communication whether or not your observation collapsed the key.

Most of the engineering effort is preserving the entanglement for farther travel from the source of entanglement.

Note: I'm using "key" here because it's presumed the shared state would refer to an encryption key, but you could use it for other types of communication (eg agreeing on a novel primary key for some common database).

Re: Sustained, high-fidelity quantum teleportation

#104

Post by tsimionescu »

ksec wrote: post #96
pontus wrote: post #75

Earlier quoted context omitted.

The receiver does not know that a message has been sent until the first person contacts them classically. It's a common mistake to think that quantum teleportation is a new way of sending information. It's really a way to use classical communication in order to leverage entanglement to bypass various limitations of quantum mechanics. So, the two people communicating would e.g. start out together and create a pair of…

Thank You. That destroy my hopes of having (Close to ) Zero Latency Communication with Quantum Teleportation / Entanglement. We are still bound by the speed of light!

Yes, all of our physics only works if we assume that there is a maximum physical speed, which only massless particles like light can even reach. QM is perfectly consistent with this well-confirmed observation.

Re: Sustained, high-fidelity quantum teleportation

#105

Post by edge17 »

CreepGin wrote: post #101
edge17 wrote: post #84

Earlier quoted context omitted.

Got it, thanks for the explanation. Also, not to get ahead of ourselves (understanding this is research), but what is the use/benefit of this method? We can already send and receive information over great distances with and without wires at seemingly high speeds. Is this a new level of speed? Are there some previous limitations of distances that are now surmountable? Is the power or cost envelope required somehow red…

I think you missed his remarks: > The receiver does not know that a message has been sent until the first person contacts them classically. It's a common mistake to think that quantum teleportation is a new way of sending information. It's really a way to use classical communication in order to leverage entanglement to bypass various limitations of quantum mechanics.

I meant more like, wireless and fiber are both classical ways to send data but each clearly has a benefit. In the same vein, does this new method have some clear benefit?

Re: Sustained, high-fidelity quantum teleportation

#106

Post by tsimionescu »

Rooster61 wrote: post #97

So, something that always bothered me, and my admittedly ignorant understanding of QM as a non-physicist. I understand that the quantum state of a particle can be teleported, and that classical information must be passed to observe the particle and collapse the state correctly. My question is, if we can't observe the particle, how do we know that that particle is entangled with the original one?

We take a process that produces entangled pairs, and send the 2 particles to different places. As long as we don't measure their state (whatever that means - TBD :) ), they remain entangled.

Re: Sustained, high-fidelity quantum teleportation

#108

Post by Rooster61 »

tsimionescu wrote: post #106
Rooster61 wrote: post #97

So, something that always bothered me, and my admittedly ignorant understanding of QM as a non-physicist. I understand that the quantum state of a particle can be teleported, and that classical information must be passed to observe the particle and collapse the state correctly. My question is, if we can't observe the particle, how do we know that that particle is entangled with the original one?

We take a process that produces entangled pairs, and send the 2 particles to different places. As long as we don't measure their state (whatever that means - TBD :) ), they remain entangled.

But that begs the question of how we know that we have produced an entangled pair. Do we not need a metric to use to make sure they are entangled?

Re: Sustained, high-fidelity quantum teleportation

#109

Post by tacon »

rd11235 wrote: post #93

This article says this result may transform communication, but seems to make no mention of why . What improvements does this have over classical communication?

One advantage of quantum communication systems is that tapping the flow is rendered essentially impossible.

Re: Sustained, high-fidelity quantum teleportation

#110

Post by bluesign »

Poc wrote: post #99
bluesign wrote: post #54

Earlier quoted context omitted.

Sorry but this example doesn't make sense, how it is faster than light?

It is not faster than light. I think what he wanted to show was a situation, in which entanglement and quantum mechanics, are superior to classical physics. i.e someone using quantum mechanics would have an advantage over someone who don't. However, as he said, in this situation the two generals could have agreed on something else, like if it was raining or not. In fact, something they could have done is to flip a co…

“ So there exist situation where we can use entanglement to achieve better results, for example in "non-local games", where players sharing entangled state can win with probability 1, when "classical player" with probability Do you have an example for this? This is really interesting
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