[Halc]

That's interesting, Halc. How would one go about demonstrating that such a particle is in a state of superposition?

I do not know the exact procedure to detect superposition of spin state, but I do know that it is a statistical thing, that it can be demonstrated only by doing the experiment repeatedly. So for instance, the photon might be in superposition of having gone through one slit and the other, but the measurement is the dot it creates on the screen which doesn't tell you anything, but 1000 dots creates an interference pattern (superposition) and 1000 dots creates a simple bell curve (not in superposition). The spin state is similar, so you'd need to have a lot of them.

[Origin]

How would one go about demonstrating that such a particle is in a state of superposition?

Here is a Youtube video that does a good job of simply explaining superposition IMO.

[paul cotter]

Hi Origin, I understand the concept of superposition but was curious how one could demonstrate such a scenario without incurring the measurement that would "break" the superposition. I rarely if ever look at videos and prefer a document I can read. Thank you anyway.

[Zer0]

I would be more comfortable saying " entanglement does not allow for faster than light communication. "

Carved on a Rock & Set in Stone.
Totally Agreed!
& Thanks for the Wording, coz it Matters.

& HiYa Halc!
Two Teachers are Better than One.

Hope Mr Cotter would join in too, Three is Definitely not a crowd.


Well, back to Q.E.

Socks got no left/right...lol true that...let's not use them.

Gloves got Pre-Determined left/right...hmm let's not use them too.

Ummm...can We Plz use a Coin.
(())
Two sides...head/tails.

We toss it up n it's spinning as an independent system.

While it's spinning, We slice n dice it in half.
((   //   ))

Both halves have a head side & a tail end.
Still spinning.

Both (2) parts of the same (1) system now in a Singlet state.
Head/Tails Undetermined.

Then we separate Them, while they are still Spinning, across a linear perpendicular path so as to avoid Decoherence.
(( - - - - - - - ))

Now we check one of Them.
Observation thru Instrumentation breaks Coherence and it Stops spinning and We see a Head.
(H(

Okay...if Everything above seems Sensible then Please lemme know & Only then shall i move ahead.

[paul cotter]

Hi Zero, there is not much I could contribute, I am just a lowly retired electrical engineer, not a physicist and my knowledge of quantum  phenomena is primitive. I have always had an interest in all areas of science but my knowledge is very patchy on this subject.

[Zer0]

Hi Zero, there is not much I could contribute, I am just a lowly retired electrical engineer, not a physicist and my knowledge of quantum is phenomena is primitive. I have always had an interest in all areas of science but my knowledge is very patchy on this subject.

If this is your Personal outlook of your Ownself, then you most certainly do Not Know Thy Self.

I have Observed you providing Corrections on posts & being Thanked for doing so.

Anyways, to continue or not is your decision & i shall Respect that.

ps - Problem with the World is, Fools are full of Confidence & Wise full of Doubts.
(Bertrand)

[paul cotter]

True enough, Zero. But the more you know the more you realise how little you know. Honestly if I could contribute more, I would without hesitation.

[Origin]

Ummm...can We Plz use a Coin.
(())
Two sides...head/tails.

We toss it up n it's spinning as an independent system.

While it's spinning, We slice n dice it in half.
((   //   ))

Both halves have a head side & a tail end.
Still spinning.

Both (2) parts of the same (1) system now in a Singlet state.
Head/Tails Undetermined.

Then we separate Them, while they are still Spinning, across a linear perpendicular path so as to avoid Decoherence.
(( - - - - - - - ))

Now we check one of Them.
Observation thru Instrumentation breaks Coherence and it Stops spinning and We see a Head.
(H(

This seems like an overly complicated analogy that can't reflect what is really going on since you are trying to use a classical system to describe a quantum system.
What question are you wishing to have answered about entanglement and communication?

[Origin]

See if this helps.

Let's look at 2 entangled particles.  We will assume that the property we are going to look at is the spin of the particles.
The 2 particles are separated by 10 million miles.  Each location has a detector that will measure the particles spin direction (up or down).
Here are the rules about the entangled particles:
1.  When an initial measurement of one of the particles is measured there is a 50-50 chance the direction will be up and a 50-50 chance the particle will be down.
2.  There is no way to predict what direction the spin will be it is completely random.
3.  When measured the particle can only be up or down.
4.  There is no way to force the particle to a certain orientation.
5.  Once either particle is measured they are no longer entangled.
6.  Once you measure the orientation of your particle you instantly know the orientation of the other particle.
7.  When either location measures their particle the result is completely random.  So if I measure my particle as up I will know that your particle will measure down, however you don't know that.  Your measurement will be completely random as far as you can tell, but once you measure our particle, you will know that my particle will be up.

Since both locations can only get a random result there is no way to use these random result to communicate.   

[Halc]

A couple of clarifications, based on my limited knowledge of the issue.

We will assume that the property we are going to look at is the spin of the particles.
The 2 particles are separated by 10 million miles.  Each location has a detector that will measure the particles spin direction (up or down).

We are measuring the spin relative to some particular axis. Only if both measurements use the same axis will the measurements be fully correlated. If perpendicular axes are used, there will be no correlation. If something between is used (45 degrees say), there will be partial correlation.

5.  Once either particle is measured they are no longer entangled.

Sort of. The measuring system is effectively entangled with the unmeasured particle, which is why you can know what the measurement will be if it ever gets done. I think if you measure a particle along the same axis twice in a row, you'd get the same result, so in that way of looking at it, the two particles remain entangled, but the entanglement is now restricted to the axis that has been chosen, so a subsequent measurement along a perpendicular axis isn't going to be correlated with the unmeasured particle.

6.  Once you measure the orientation of your particle you instantly know the orientation of the other particle.

You instantly know the outcome of a measurement of the other particle along the same axis, regardless of if it has already been done or will be done (a frame dependent distinction). The far guy of course knows none of this, so from his point of view, the outcome is still totally random.
Anyway, your wording implies that the unmeasured particle actually has a spin orientation, which most interpretations deny.


All that said, the glove analogy (a classical example) still satisfies pretty much all of the above points. I separate the gloves in envelopes unopened, When one is opened, that person instantly knows the contents of the other envelope. It's a epistemological thing, not a metaphysical one. The glove system is classical, so metaphysically, there is in fact a left glove in this envelope and a right in the other. No superposition. We just don't know which is which.

Quantum systems go further than that. The EPR paradox showed that quantum entanglement cannot be classical like the gloves. I'm not going to attempt to explain that since I'd get it wrong. Look up the paradox or Bell's theorem if you want the detail. They are probably well beyond what Zero want's to know. They are beyond my capability to convey correctly without just copying text from a website.

[Origin]

We are measuring the spin relative to some particular axis. Only if both measurements use the same axis will the measurements be fully correlated. If perpendicular axes are used, there will be no correlation. If something between is used (45 degrees say), there will be partial correlation.

The particle is measured by applying a magnetic field.  The measurement will detect if the spin is up, aligned with the direction of the field or if it is down, aligned opposite of the field direction.  Therefore the orientation of the lab frame is not important.

I think if you measure a particle along the same axis twice in a row, you'd get the same result,

That is not an aspect of entanglement.  For instance if you measure the spin of any quantum particle as up and then measure it again it will measure up again 100% of the time.

so in that way of looking at it, the two particles remain entangled, but the entanglement is now restricted to the axis that has been chosen, so a subsequent measurement along a perpendicular axis isn't going to be correlated with the unmeasured particle.

This is not correct.  The particles are no longer entangled.  When 2 particles are entangled they have the same wave equation.  When one of the particles is measured the wave function collapses and now the particles are no longer described by a single wave equation, now both of the particles are described by different wave equations.

All that said, the glove analogy (a classical example) still satisfies pretty much all of the above points.

Agreed. 

[Halc]

The particle is measured by applying a magnetic field.  The measurement will detect if the spin is up, aligned with the direction of the field or if it is down, aligned opposite of the field direction.  Therefore the orientation of the lab frame is not important.

It is the orientation of the field that is important. That defines the axis of measurement. It has nothing to do with choice of abstract coordinate system (lab frame).

This is not correct.  The particles are no longer entangled.  When 2 particles are entangled they have the same wave equation.

Good point. The wave functions (at least that concerning their spin) are different now. Other parts (wave function of position say) were never the same, even though they were spin-entangled. You can't say that two entangled particles millions of miles apart are equally likely to be found at a given location.

  When one of the particles is measured the wave function collapses and now the particles are no longer described by a single wave equation, now both of the particles are described by different wave equations.

[Zer0]

This is Exactly what i was Wishin for...a Detailed discussion.

Thank You both & Please continue.

ps - I'm all set, switched on potato mode, crashed on bean bag, pack of crispy chips in one hand & a slurpy cola in the other.
( I'm Lovin it! )

[Zer0]

Hmm...shows over eh?
Bummer!

Well, i think I'll have to ditch my simple coin analogy & step into your socks to get some Answers...

Okay.
How do We know or how can We confirm 2 particles obtained from 1 system have reached or are in a Singlet State?

w.r.t. Electrons being paired, is it an Assumption?

Or is it that a Million Q.E. measurements made shall Always provide a 100% deterministic result bcoz of Conservation of Angular Momentum?