B Quantum teleportation of usable information

[Isaac Hart]

Influencing electrons angular momentum​

You can use magnetic fields to influence the intrinsic value of angular momentum (spin). When an electron interacts with a magnetic field it experiences a force known as torque – twisting force in the direction of the magnetic field. Therefore, if you pass an entangled electron through a magnetic field its angular momentum it changes to that of the direction of the field. And so, the entangled partner of that electron will be more likely, once observed, to be in the opposite spin direction of the magnetic field. This means that you can use magnetic fields at point A to influence the observation at point B. The impact however of magnetic fields is probabilistic and not definite, meaning that that to control the observation at point B you must observe the spin of at least 100 different electrons. This would mean that the impact at point A as a clear impact on the state of the spin at point B.

Overall, this means that from one point to another you can manipulate the outcome or observation instantaneously. This means that you would be able to quantum teleport usable information. By using a series of logic gates, you could send messages from one location to another, the process would be costly, and the infrastructure does not currently exist. However, theoretically in the future you would be able to have faster than light communication / travel.

 

[Nugatory]

Overall, this means that from one point to another you can manipulate the outcome or observation instantaneously. This means that you would be able to quantum teleport usable information. By using a series of logic gates, you could send messages from one location to another, the process would be costly, and the infrastructure does not currently exist. However, theoretically in the future you would be able to have faster than light communication / travel.

Nope, doesn’t work.
You can Google for the “quantum non-communication theorem”, or read some of our many many threads on why it work.
Please do this and make a good-faith attempt to understand why it won’t work before you continue this thread.

 

[PeterDonis]

When an electron interacts with a magnetic field it experiences a force known as torque – twisting force in the direction of the magnetic field.

This is a classical description, not a quantum description. You can't mix classical and quantum models; it doesn't work.

 

[Vanadium 50]

This means that you can use magnetic fields at point A to influence the observation at point B.

Not in the way you are thinking. No value of the field at A influences the particle at B.

 

[DrChinese]

The impact however of magnetic fields is probabilistic and not definite, meaning that that to control the observation at point B you must observe the spin of at least 100 different electrons. This would mean that the impact at point A as a clear impact on the state of the spin at point B.

Assuming entanglement worked this way (which it doesn't):

You could do this to 100 electrons. At point B, you see 100 random results of up> and down>. This is regardless of what is done (or not done) at point A. Not a lot of useful information in random bits.

It is only the correlation between A and B results that shows a pattern. You need normal light speed communication to perform the correlation. (But even then, as the others above correctly point out, you still cannot send a message.)

 

[Isaac Hart]

This is a classical description, not a quantum description. You can't mix classical and quantum models; it doesn't work.

When an electron with an intrinsic magnetic moment (due to its spin) encounters an external magnetic field, it experiences a torque.
The torque tends to align the electron’s magnetic moment with the direction of the magnetic field.
Imagine the electron’s magnetic moment as a tiny spinning top. The external magnetic field causes the top to precess around the field direction.

• Quantum mechanics tells us that an electron’s spin is quantized. It can have only specific values.
• The two possible spin states are often denoted as “spin up” and “spin down.”
• These states correspond to the electron’s magnetic moment being aligned either parallel or antiparallel to the magnetic field.

 

[Isaac Hart]

Assuming entanglement worked this way (which it doesn't):

You could do this to 100 electrons. At point B, you see 100 random results of up> and down>. This is regardless of what is done (or not done) at point A. Not a lot of useful information in random bits.

It is only the correlation between A and B results that shows a pattern. You need normal light speed communication to perform the correlation. (But even then, as the others above correctly point out, you still cannot send a message.)

Thanks for the feedback. However, what i am talking about is how the colapse of the wavefunction at point A influences the colapse of the wavefunction at point B. Therefore, by using the magnetic fields to make the spin state of electron A be more probable to be up you would make the spin state at position B to be more probably up.

 

[Isaac Hart]

Not in the way you are thinking. No value of the field at A influences the particle at B.

Thanks for the feedback. But I am talking about the entanglement or corrolation between the electrons, if at point A it is up than at Point B it is down. therefore of course the state of elecetron A influences the state of electron B.

 

[Isaac Hart]

Nope, doesn’t work.
You can Google for the “quantum non-communication theorem”, or read some of our many many threads on why it work.
Please do this and make a good-faith attempt to understand why it won’t work before you continue this thread.

Please explain why it wont work, I would like to learn

 

[Vanadium 50]

if at point A it is up than at Point B it is down.

Not if you rotate one of tnem with a magnetic field.

 

[Isaac Hart]

Not if you rotate one of tnem with a magnetic field.

Surely it would as before oberservation their angular momentum remains a superposition

 

[weirdoguy]

Please explain why it wont work, I would like to learn

Why would he explain if he explicitly asked you to do the research yourself? Did you google suggested phrase?

 

[Isaac Hart]

I would just prefer an explanation from a real person rather than a webpage, I like to discuss ideas and controdictions. Isn't that the point of this website?

 

[Vanadium 50]

Surely it would as before oberservation their angular momentum remains a superposition

Not once you flip one of them over. If you have a pair of socks and dye one, does the other change color too?

 

[PeterDonis]

When an electron with an intrinsic magnetic moment (due to its spin) encounters an external magnetic field, it experiences a torque.
The torque tends to align the electron’s magnetic moment with the direction of the magnetic field.
Imagine the electron’s magnetic moment as a tiny spinning top. The external magnetic field causes the top to precess around the field direction.

• Quantum mechanics tells us that an electron’s spin is quantized. It can have only specific values.
• The two possible spin states are often denoted as “spin up” and “spin down.”
• These states correspond to the electron’s magnetic moment being aligned either parallel or antiparallel to the magnetic field.

You are just repeating the thing I already told you was wrong, namely, mixing a classical and a quantum description. That won't work.

I would just prefer an explanation from a real person rather than a webpage

Then you should stop repeating things that you have already been told are wrong. And you should start asking questions instead of making statements. The first post of yours in this thread that even contains a question at all is post #13, and that question is clearly rhetorical.

 

[PeterDonis]

I would just prefer an explanation

An explanation of what? Your thread title talks about quantum teleportation, but so far you have not said anything about quantum teleportation that can actually be explained, since none of your assertions contain any correct statements about quantum teleportation.

Instead of just making assertions, a better procedure would be to give a reference to a textbook or peer-reviewed paper that says something about quantum teleportation that you want an explanation of, and then ask about it. Can you do that?

 

[Isaac Hart]

You are just repeating the thing I already told you was wrong, namely, mixing a classical and a quantum description. That won't work.


Then you should stop repeating things that you have already been told are wrong. And you should start asking questions instead of making statements. The first post of yours in this thread that even contains a question at all is post #13, and that question is clearly rhetorical.

I am only trying to argue my point of view, I would like you to explain how it is a classical description and not a quantum description. I have been told why my ideas are wrong, however I would like to know why they are wrong. I am a 15 year old who is interested in quantum mechanics, I have no access to any other papers about quantum teleporation. I had an idea that I thought was cool and so I thought id share it on this quantum mechanics Physics Forums webpage. My physics teacher said that I should gather feedback on my idea, please explain how it is an example of mechanical physics rather than quantum physics. Most other sources suggest that it is a quantum feature rather than one based on mechanical physics.

I thought that:

• Quantum mechanics introduces the concept of quantization. The electron’s spin can exist in discrete states.
• Unlike classical objects, electrons can be in a superposition of states (e.g., both “spin up” and “spin down” simultaneously).
• The torque affects this superposition, leading to changes in the probabilities of different spin states.
• The interaction with the magnetic field can cause Larmor precession, where the electron’s spin precesses around the field.
• Coherent control of this precession allows us to manipulate the electron’s spin state precisely.

Please explain why I am wrong

 

[PeterDonis]

I am only trying to argue my point of view

That is not what PF is for. PF is for helping people to understand mainstream science. It is not for people to argue their personal points of view.

I would like you to explain how it is a classical description and not a quantum description. I have been told why my ideas are wrong, however I would like to know why they are wrong.

That is not something we can do within the scope of a single PF discussion. (See further comments below.) That said, I'll try to give brief responses to your bullet points in a separate post following this one.

I am a 15 year old who is interested in quantum mechanics

The fact that you are interested is great! However, the best way to exercise your interest is not to try to come up with a personal point of view on your own, without any basis in current mainstream science, and then come to an Internet forum and ask people to explain to you why it is wrong. That is a very inefficient use of time and energy, both for you and for the people you are asking to help you.

The best way to exercise your interest is to first make use of the huge volume of material that is available to you in the form of textbooks and papers (yes, you can find these for free on the Internet, see further comments below) to study the subject, work the problems that the textbooks give you, and build your understanding that way. That will first of all be a lot more efficient, and second will give you a much better basis for asking questions when it is appropriate to do so, because you will be able to base your question on material that has been tested and reviewed, so it will be much easier for people you ask to help you, to actually help you.

I have no access to any other papers about quantum teleporation.

Sure you do. You can find lots of papers on arxiv.org. You can also find lots of university course materials available for free online (for example on the MIT OpenCourseware site). You might also be able to find textbooks online.

 

[PeterDonis]

I thought that

The first question is, why do you think any of these things? What is the basis for your information? Where did you get it from? Providing that background is crucial if you want people to help you.

• Quantum mechanics introduces the concept of quantization. The electron’s spin can exist in discrete states.

First, only some observables are quantized. Spin is, but position and momentum of a free particle, for example, are not.

Second, "quantization" is not actually a basic concept in QM! QM was not formulated by people saying, hey, let's see what happens if we quantize things. Quantization just happened to be a consequence of QM for certain observables under certain conditions, which for historical reasons gave its name to the entire field.

• Unlike classical objects, electrons can be in a superposition of states (e.g., both “spin up” and “spin down” simultaneously).

Superposition by itself doesn't mean much, since it is, in the jargon of QM, basis dependent. For example, say I have an electron whose spin state is a superposition of "spin up" and "spin down" about a certain axis. There will be some other spin axis for which that same electron, in the same state, will always give "spin up" on measurement. So if I choose that other spin axis, I can describe the same electron in the same state as not being in a superposition.

The really non-classical thing QM introduces is entanglement, which is something different from "superposition" and is not basis dependent. See further comments below.

• The torque affects this superposition, leading to changes in the probabilities of different spin states.
• The interaction with the magnetic field can cause Larmor precession, where the electron’s spin precesses around the field.

Under certain conditions, yes, the time evolution of an electron's spin state in a magnetic field will lead to a change in the coefficients of "spin up" and "spin down" in its state, assuming you keep your basis fixed. But that is all a mathematical abstraction unless and until you measure the electron. You can't observe the torque "twisting" the electron the way you can in classical mechanics. Indeed, if you try to measure the electron, you will disrupt the smooth "twisting" behavior due to the torque, and can even prevent it from happening--this is called the "quantum Zeno effect".

• Coherent control of this precession allows us to manipulate the electron’s spin state precisely.

More precisely: if you let the precession happen for a precisely controlled time, you can induce a precisely controlled change in a single electron's spin state. But note, once again, that you are not measuring the spin state. You are just letting a certain effect happen for a certain time and predicting that it will induce a certain change in the electron's spin state. Indeed, as noted above, you can't measure the electron's spin while you are doing this, because it will spoil the effect. So it's not the same as classical mechanics, where you can observe such things while they happen without affecting them.

Now, having said all that: none of it has anything at all to do with entanglement or quantum teleportation. To show the existence of entanglement, or to do quantum teleportation, you have to make measurements of spin. (You can in principle do this with electrons, but actual experiments use photons because they are much easier to deal with. Photon polarization, for this particular application, can be treated similarly to electron spin.) And notice that nothing I said above was about entanglement at all. I was only talking about single electrons.

If you have two entangled electrons (or photons), A and B, and you use processes like the above to manipulate the state of A, you cannot say that you are "simultaneously" manipulating the state of B. You aren't. All you are doing is manipulating the state of A. Those operations do nothing to B. (Indeed, quantum computing experiments rely on this fact, that if they put qubit A through a particular gate, it doesn't change anything about qubit B.) You can measure A, and measure B, and see from the correlations between the measurement results that they are entangled. But you cannot "instantly" affect B by anything you do to A. That's not how entanglement works.

 

[PeterDonis]

This thread is now closed. The OP is encouraged to start a new thread when they have a better basis for asking questions.