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Sustained, high-fidelity quantum teleportation

news.fnal.gov

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Re: Sustained, high-fidelity quantum teleportation

#131

Post by whatshisface »

tsimionescu wrote: post #115
whatshisface wrote: post #67

Earlier quoted context omitted.

You're not going to get that data back out, though. When you measure 50 qbits, you get 50 bits, and you destroy the state irrecoverably.

Per the wikipedia page, the protocol provides both encoding and decoding, and there have been experimental realizations that successfully retrieved the original message. Is the article inaccurate?

The parent comment was talking about data compression, the article is talking about copying a quantum state. Data compression will not work because you can't read a quantum state into classical information.

Re: Sustained, high-fidelity quantum teleportation

#132

Post by Twirrim »

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…

If classical communication is still needed to this degree, what value does this approach bring vs classical communication?

The dependency on classical communication would imply that it's not lower latency or higher throughput, and will remain subject to signal loss or degradation.

Re: Sustained, high-fidelity quantum teleportation

#133

Post by ahelwer »

Twirrim wrote: post #132
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…

If classical communication is still needed to this degree, what value does this approach bring vs classical communication? The dependency on classical communication would imply that it's not lower latency or higher throughput, and will remain subject to signal loss or degradation.

It's the only way to reliably communicate a quantum state. Want to network quantum computers? This is how you do it.

Re: Sustained, high-fidelity quantum teleportation

#134

Post by ahelwer »

mrfusion wrote: post #34
nabla9 wrote: post #12

context: Using term teleportation makes sense in the quantum realm. No-cloning theorem in quantum physics says that it's impossible to do exact copy of unknown quantum state. But it turns out that you can teleport it when the original state is destroyed. You can't have exact `cp` command for the quantum state, only `mv`. If this makes you think linear logic, you are right.

So that could neatly solve the philosophical teleportation problem? Ie if you teleport and the original isn’t destroyed. Which one are you?

This problem is only a problem if you assume you exist in some persistent sense, rather than being a continuously-arising emergent phenomenon of your physiology.

As for whether the no-cloning theorem informs this, there isn't any reason to believe consciousness is related to quantum mechanics.

Re: Sustained, high-fidelity quantum teleportation

#135

Post by jv22222 »

pontus wrote: post #7
sreejithr wrote: post #3

Does this mean information can be transmitted faster than light speed?

No, while entanglement acts instantaneously across a large distance, there's no way for that "signal" to carry any information. In order to complete the teleportation the two parties must somehow communicate in order to convey an additional piece of information. This communication would be classical and slower than light.

Whey can't they just have an agreed upon stop point?

Like, keep parsing the incoming information until you see a period (for example).

(I know it's not using actual characters, just using the idea to illustrate the point).

Re: Sustained, high-fidelity quantum teleportation

#136

Post by Buttons840 »

pontus wrote: post #5
sabellito wrote: post #2

I'm confused, as I'm an enthusiast but definitely no physicist. The article states that quantum information is being teleported via entanglement. However, it was my understanding that one cannot transfer information in such a way as the "information" is only revealed when interacting with the particle. Could someone perhaps clarify what's going on?

You entangle two systems but in order to actually complete the teleportation you need to measure one system and then convey the outcome of that measurement to the other party. This information is needed by the second party in order for them to be able to correctly collapse the state of their system into one that is identical to the original system being teleported. The information that the first party must convey to…

ELI5: I have a red ball and a blue ball. I randomly place each ball into one of two boxes. I give you one box, and keep the other box for myself, then wave my magic wand and transport you 5,000 light years away.

You look inside your box and see a red ball. In that moment you learn that I have a blue ball in my box. You gained that information in an instant, about a box 5,000 light years away.

(This is an explanation I've heard. But I don't personally know if it's accurate.)

Re: Sustained, high-fidelity quantum teleportation

#137

Post by chiefofgxbxl »

Buttons840 wrote: post #136
pontus wrote: post #5

Earlier quoted context omitted.

You entangle two systems but in order to actually complete the teleportation you need to measure one system and then convey the outcome of that measurement to the other party. This information is needed by the second party in order for them to be able to correctly collapse the state of their system into one that is identical to the original system being teleported. The information that the first party must convey to…

ELI5: I have a red ball and a blue ball. I randomly place each ball into one of two boxes. I give you one box, and keep the other box for myself, then wave my magic wand and transport you 5,000 light years away. You look inside your box and see a red ball. In that moment you learn that I have a blue ball in my box. You gained that information in an instant, about a box 5,000 light years away. (This is an explanation…

(My understanding; I only took one course in quantum mechanics)

Arguably the information that you "gained" was predetermined when you decided which colored ball to place in which box. You didn't gain any knowledge that you couldn't have known before you were teleported 5,000 ly away.

What's also more difficult is that the balls wouldn't have definitive colors, but exist in a probabilistic state / superposition. But you couldn't send the message "I have a red ball" to the individual 5,000 ly away because collapsing your ball's wave will be random and you can't determine which color you want. You could "mistakenly" collapse your ball to blue, not red.

Re: Sustained, high-fidelity quantum teleportation

#138

Post by pontus »

Buttons840 wrote: post #136
pontus wrote: post #5

Earlier quoted context omitted.

You entangle two systems but in order to actually complete the teleportation you need to measure one system and then convey the outcome of that measurement to the other party. This information is needed by the second party in order for them to be able to correctly collapse the state of their system into one that is identical to the original system being teleported. The information that the first party must convey to…

ELI5: I have a red ball and a blue ball. I randomly place each ball into one of two boxes. I give you one box, and keep the other box for myself, then wave my magic wand and transport you 5,000 light years away. You look inside your box and see a red ball. In that moment you learn that I have a blue ball in my box. You gained that information in an instant, about a box 5,000 light years away. (This is an explanation…

I talked about this elsewhere in this thread (just with gloves instead of colored balls).

Re: Sustained, high-fidelity quantum teleportation

#139

Post by thwd »

jv22222 wrote: post #135
pontus wrote: post #7

Earlier quoted context omitted.

No, while entanglement acts instantaneously across a large distance, there's no way for that "signal" to carry any information. In order to complete the teleportation the two parties must somehow communicate in order to convey an additional piece of information. This communication would be classical and slower than light.

Whey can't they just have an agreed upon stop point? Like, keep parsing the incoming information until you see a period (for example). (I know it's not using actual characters, just using the idea to illustrate the point).

You have a box with random garbage in it. I have a box with a football in it. We entangle the football and the garbage. You stand far away from me. If you randomly open your box now, you may either see a football or random garbage. If I call you on the phone (classically) and tell you to open the box tonight at precisely 8:12pm, you're guaranteed to find a football then and hence, I will have the garbage.

There's no parsing; it's all or nothing.

Re: Sustained, high-fidelity quantum teleportation

#140

Post by im3w1l »

junon wrote: post #20
pontus wrote: post #5

Earlier quoted context omitted.

You entangle two systems but in order to actually complete the teleportation you need to measure one system and then convey the outcome of that measurement to the other party. This information is needed by the second party in order for them to be able to correctly collapse the state of their system into one that is identical to the original system being teleported. The information that the first party must convey to…

This makes zero sense. If the information must be conveyed classically anyway, what's the point?

Suppose Alice and Bob have a pair of entangled particles. But Bob wants to give his part of the pair to Charlie.

Quantum teleportation lets him do that over the phone.

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