# Time and information

Discussion in 'Physics & Math' started by arfa brane, Jan 14, 2022.

1. ### Beer w/StrawTranscendental Ignorance!Valued Senior Member

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Do you have an experiment?

3. ### arfa branecall me arfValued Senior Member

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I'm toying with the idea of quantum teleportation not being an actual transmission, which seems reasonable given it can occur 'instantaneously' depending on when measurements are made, and by who, how they measure their states is also important. A protocol is necessary, and there are steps to follow in a time-ordered sequence.

But entangled particles stay entangled over time, unless they interact with other particles. That's a rule of entanglement--they don't care about time, only interactions. The intelligent senders and receivers in the teleportation of "quantum information" have to know a lot about not just their particle, but a whole system of them.

Because of what is known, and because they have to communicate at some step in a classical way, this implies that information has been sent "instantly", but I say it's already there, you can't do it like that.
Since that's the only other option, right?

5. ### arfa branecall me arfValued Senior Member

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There's a way to introduce the Alice and Bob thing into the above diagram (but of course, you knew that), so Alice gets one, Bob the other of a pair of Bell-state 'particles'.

In the diagram, these correspond to one of q1 or q2, since these go through an 'entanglement' circuit which is leftmost in the diagram, so "happens" first; check.

So which goes to which? That depends on how you interpret the rest of it. In the abstract, you want to put something else in the diagram to represent the transport of q1 away from q2, presumably that's going to take . . . time so try to add a bit of detail.

Alice contends she has transmitted a pair of classical bits to Bob. Why, or how can she so claim?
Do we need a boy scout to explain the measurement part of the circuit here?

7. ### Beer w/StrawTranscendental Ignorance!Valued Senior Member

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Why post something like this unless you have a particle accelerator ?

8. ### Write4UValued Senior Member

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Brian Greene seems to think it is possible, theoretically.

9. ### arfa branecall me arfValued Senior Member

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My particle accelerator is in the shop at the moment. I'll just have to keep using my quark spanner.

10. ### arfa branecall me arfValued Senior Member

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I don't know about you guys, but I'm fascinated by the current developments. Especially when new materials and not-seen-before effects are popping up so fast, understanding "new" stuff takes some catching up. It seems safe to say that we haven't exhausted the ways particles interact with each other, we haven't seen all the quasiparticles in the strange zoo either.

Did you know an electron can be represented by an equation that says it is two distinct quasiparticles, one carries all the momentum, the other has all the charge. Meet magnons and chargons, about to do battle on a graphene monolayer near you!

Are you not entertained?

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Well, I am.

12. ### arfa branecall me arfValued Senior Member

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Notes on the ideas of time dependence and time independence.

The appearance of an interference pattern is time dependent. Independently of time, the probability amplitudes are guaranteed to produce a (statistical!) pattern; there is a probability of 1 that a pattern will appear (the message will be received . . .), given a fair sample.

In the posted diagram, time "flows" left to right. The vertical direction is independent of time; this is where combinations of operations, on those amplitudes, generate product states such as a maximally entangled pair.

To see what that is in the context of the diagram you need to see part of it as a 2-input, 2-output gate, what goes in has to come out, you can't erase anything by "reading" it. What comes out has a different phase relative to what went in and this has to work in reverse (even if you don't reverse anything).

One way to see why there is a global phase is, you can build a circuit that gives a state an unknown phase, equivalent to rotating it to a 'global state'.

Last edited: Jan 22, 2022
13. ### arfa branecall me arfValued Senior Member

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Do single electrons become entangled with a double slit? The pattern that appears, even when electrons are transmitted one at a time, implies that at the 'output' there is a pair of simultaneous wavefronts, just as a classical wavefront at the 'input' would produce.

So we can at least draw this model without being too embarrassed about it. We can also postulate that single electrons somehow encode "which slit" they passed through, or that they carry path information. Since nothing more definitive can really be said about what happens between the "gate" operation and the screen, without measurements.

Simultaneous events seem to be an important part of the play, here. For instance it is very much a part of measurements in the relatively new quantum optics; oddly, noise can play a part in the statistics, in that a little bit of noise is a good thing. I recommend a look at the history of this stuff, and some guys called Hanbury Brown, and Twiss.

p.s. that phase thing, a phase is usually represented by an angular difference (in radians); in the Bloch sphere a phase is a complex angle. A phase difference represents a difference between probability amplitudes. Simple eh?

Last edited: Jan 22, 2022
14. ### SarkusHippomonstrosesquippedalo phobeValued Senior Member

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I appreciate that much of this thread is just your stream of consciousness on the matter, but you seem to be losing coherence...
How do you think a single electron becomes "entangled"?
What do you think it becomes entangled with? Itself???
Why do you think the double-slit interference pattern has anything to do with entanglement, rather than wave-particle duality?

Of course, you could run the experiment with entangled particles, but the process of entanglement itself is separate.
You mean a model with single electrons being entangled? Nah, you should probably be quite embarassed about it.

Honestly, I think this thread is getting nearer the cesspool every time you post in it. Or at least to the "Free Thoughts" forum.

15. ### Write4UValued Senior Member

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Are you familiar with Bohmian Mechanics? Bohm postulated that electron are physical particles riding a universal "pilot wave".

The de Broglie – Bohm theory as a rational completion of quantum mechanics,

Couder experiments,[1][2] "materializing" the pilot wave model.

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

16. ### DaveC426913Valued Senior Member

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Strange, my opinion is about as opposite as it can get. This thread is actually about physics.

I'm following along even though some of it is beyond my knowledge of entanglement.

Last edited: Jan 22, 2022
17. ### arfa branecall me arfValued Senior Member

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Working backwards:

Why do you think an electron can't, or can be in superposition of a wave and a particle? Why can an electron simultaneously occupy two orbitals around a Hydrogen nucleus, with equal probability? Oh wait, I guess Schrodinger, Einstein, et al had a problem with it too.

How do you think an electron is entangled with anything (another electron, two paths, . . .) and do you see any relation to superposition?

Of course. So what would a quantum gate diagram look like, for this experiment? What would you expect to get, in terms of classical measurements?

Last edited: Jan 23, 2022
18. ### arfa branecall me arfValued Senior Member

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I'm strangely unembarrassed with the idea that an electron approaching a pair of slits is in a superposition of wave and particle, which nonetheless has a "probability amplitude", and I can represent this with a straight line, perpendicular to the electron's motion. Since I get an interference pattern, I infer this single "wavefront" generates two spherical wavefronts as it passes through the two slits, or that it's just Huygen's principle in action. I don't need to see any physical waves to infer all that.

The superposition thing is what glues this baby together.

So here's my suggestion: understand first what superposition really is, then look at entanglement. You will find that entanglement is caused by particles interacting, and that's it.

An electron interacts with a pair of slits, these are systems of particles, ergo, there is entanglement.

p.s. I also think entanglement doesn't really make sense with less than two particles (resp. systems of particles).

A single particle can be in a superposition of states; this was the first "disturbing" surprise for Schrodinger. Two particles can be in a superposition of states too, but now you also have entangled "measurement operators". That is to say, Alice, Bob, and whoever else, are all systems of particles entangled with . . . the measurement basis (??)

Lest we forget, the electron (or beam of), is being measured at the slits; it's a quantum measurement--so we aren't entangled with the measurement, although we can see there's a pair of slits (??).

Last edited: Jan 23, 2022
19. ### arfa branecall me arfValued Senior Member

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One of the questions Schrodinger asked was: "if an electron can be like a wave or like a particle, can two electrons be like a larger wave? Is there an increase in the amplitude, or, you know, what?"

As we know, with electrons they diffract like any small enough object does, at one, two or more slits in a "slit interferometer". Each electron has the same probability amplitude, the only variable is beam intensity. So there is no increase in amplitudes; the pattern does however appear in less time than firing particles one by one.

Note that when Schrodinger found his mathematical solution to Hydrogen orbitals, entanglement protocols were hard to find. But here's the thing, in Hydrogen, the proton can be said to be measuring the electron's state, continuously. That's the quantum information version of why electrons orbit protons.

20. ### arfa branecall me arfValued Senior Member

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I wonder what Einstein, Podolsky, and Rosen would have thought of this diagram, once someone explained what it was? Dirac notation didn't exist back then, but I'm sure those guys would have picked it up no trouble.

That's this one: (from an o/l video about quantum teleporting)

It uses colors to distinguish different particle states (in QIS the other word for particle is qubit, which can also be a "small" system of particles, like a molecule, say).

Carla in the middle, is the only observer who sees any classical measurements. The whole thing is about who knows what, and when, apart from all the quantum "data-manipulations". Are we good here?
A rule to apply to the inputs: there are four colors which don't change, but for instance, after the H gate acts on Mr Blue, he isn't zero any more (in the so-called measurement, or computational basis).

Another zinger: firing an electron towards a pair of slits means giving it a velocity. Therefore this constitutes a measurement of the state of the electron.
It seems no detail is too small when you want to manipulate the universe like this.

Last edited: Jan 23, 2022
21. ### arfa branecall me arfValued Senior Member

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The teleportation of quantum information: you notice this is defined in more than one way. A state can be transported if it's carried by a real particle, this means the state of a particle is transferred to another, without copying the state; the other way is to manipulate entangled particles, using "spooky action at a distance".

But this "spooky" action still can't be independent of transmission of real particles with real energy; real classical information needs to either be known already (there is an agreed protocol for messaging between observers), or be transmitted, with all the physical problems that introduces, mostly called noise or signal interference/degradation, or whatever).

If two observers each have a particle, and that's all they know, there is no protocol; you need the two observers to have classical information, and decide when they get it. It's about making choices and ordering them in time.

I conclude that therefore, the appearance of an instantaneous transmission between entangled particles, is actually choice--we get confused about how this is made, possibly.

22. ### arfa branecall me arfValued Senior Member

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After staring at some diagrams, I've decided they're all actual graphs. Each 'gate' is also a Feynman diagram. Conceptually, the colored lines define distinct particles whose states may change (if they interact at a Feynman vertex with another particle). The vertical lines are a bit confusing, therefore, because they imply that real particles are transmitted in no time.

Maybe this transmission/transport should be notated somehow. Or just assume the vertical lines imply this transport from one observer frame to another. What do the dotted lines mean? They mean the particle is in an unknown state, like electrons are after they make a dot on a screen--they have an unknown position and momentum, although the mark made on the screen says "an electron was here".

So a dotted line that continues to the right, from say the orange line, implies that in Alice's frame nothing is known about the orange qubit from that point. Or perhaps, nothing can be known at all about it, would be a safer option. However, if Alice knows that Carla "should" receive it, then Carla will be able to transmit information about Mr Orange back to her.

Also, Feynman diagrams underline that a particle interacting with a field is interacting with at least one other particle.

Last edited: Jan 23, 2022
23. ### SarkusHippomonstrosesquippedalo phobeValued Senior Member

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Boiling turds on a cooker could also be classed as cooking, I guess.

It's a stream of consciousness more than any coherent point, argument, or position. And he's trying to link concepts that aren't: superposition and entanglement are very different: entanglement, at its core, is about two things that are inexorably linked: alter one and you necessarily alter the other. Typically it refers to two particles who between then have a net property that is constant, such as spin. So if you add spin to one, the other is reduced by the same, etc.
Superposition is about a quantum system being in multiple states at the same time... Until observed when it collapses to a single state.
The two phenomena are not linked, other than both being quantum phenomena.

As for the whole information matter, just Google quantum entanglement and FTL communication to get a good idea of the issue, as that seems to be the context of entanglement and information gets most airplay.

But, look, if you're happy with someone simply waffling about quantum mechanics, with no real structure to his posts, and making allusions to nonsense, then okay. I'll leave you to it.