[Vern]

I sure don't know the answer.

[JP]

Does resolving the sender system actually resolve the receiver system, or does it just restrict the possible state of the receiver system so that when it's eventually resolved it can only resolve in to one possible state, dictated by the outcome of resolving the sender system?

Is there a measurable difference between these two outcomes?  Philosophy aside, QM is about predicting the values of measurements.  It seems to me that in both cases, you know with 100% certainty that the measurement has to give you the resolved state.

[LeeE]

What I was wondering about is that it's the act of measuring the state that resolves the state, as I understand it.  So although the first system may have been measured, and as a consequence, had it's state resolved, the second system has not yet been resolved and it will not be resolved until measured, at which point it can only resolve in to one possible state because of the entanglement.  Thus it is only the possible state for the second system that is conveyed instantly.

[yor_on]

What I was wondering about is that it's the act of measuring the state that resolves the state, as I understand it.  So although the first system may have been measured, and as a consequence, had it's state resolved, the second system has not yet been resolved and it will not be resolved until measured, at which point it can only resolve in to one possible state because of the entanglement.  Thus it is only the possible state for the second system that is conveyed instantly.

If you find the answer to that one I would love to hear it LeeE.
And I think it should be worth a Nobel price:)

I should know.
I'm a Swede:

[Chemistry4me]

I should know.
I'm a Swede:

And what is that supposed to mean? Are you getting complacent yor_on?

[yor_on]

What?
With you around:)

No chance of that:

[Chemistry4me]

Good good, that is good to hear!

[swansont]

After going through the data several times I still haven't determined how they discover that the two ions are entangled. I guess one would need to study the original paper to fully understand.

The two ions are excited and can decay in two possible ways (two colors).  The emitted light for both is sent through beamsplitters, so you don't know which ion gave which photon (two paths).  There is one combination of photons and paths where you don't know which ion is in which state, and this uncertainty is the same as saying they are entangled in a superposition of the two.

http://www.sciencedaily.com/releases/2009/01/090122141137.htm

[Vern]

The two ions are excited and can decay in two possible ways (two colors).  The emitted light for both is sent through beamsplitters, so you don't know which ion gave which photon (two paths).  There is one combination of photons and paths where you don't know which ion is in which state, and this uncertainty is the same as saying they are entangled in a superposition of the two.

Okay; I spent another few minutes going over the article. I can understand that if you look at the state of one of the entangled ions, you then know the state of the other. But it looks like getting the ions into the entangled state requires processes that are limited to c.

[yor_on]

Ok, reading "There is one combination of photons and paths where you don't know which ion is in which state, and this uncertainty is the same as saying they are entangled in a superposition of the two." gave me a slight dizziness.

For me a entanglement primarily is when you split one wave into two.
This experiment seems if it is correct allow us to 'blend' as many 'waves' we like inside that beamsplitter and call the result entangled?

Does this mean that the absence of knowledge will be entanglement, and 'information'?
I have definite problems understanding the explanation given in the article
It is rather 'sloppy' writing there it seems.

Or I am really thick:)

Let us take a look on this experiment again.
We have two Ions (= electrons missing, or, being to many for a given atom) 'A' and 'B'
'A'  gets exited so it it is in a 'super position', meaning that it has a possible 50/50 chance of being in a given state (a or b, sort of).
Then we excite both Ions 'A' and 'B' and both releases one photon.
Those wander through a fiber-optic cable and 'meets', coming from opposite sides, to a beamsplitter.

So what is a beamspitter then?
"A beam splitter is an optical device that splits a beam of light in two.
In its most common form, a cube, it is made from two triangular glass prisms which are glued together.
The thickness of the resin layer is adjusted such that (for a certain wavelength)
half of the light incident through one "port" is reflected and the other half is transmitted.
Polarizing beam splitters use birefringent materials, splitting light into beams of differing polarization.

Another design is the use of a half-silvered mirror.
This is a plate of glass with a thin coating of aluminum (usually deposited from aluminum vapor).
With the thickness of the aluminum coating such that, of light incident at a 45 degree angle,
one half is transmitted and one half is reflected.
Instead of a metallic coating, a dielectric optical coating may be used.
Such mirrors are commonly used as output couplers in laser construction."

In this case it is easier to understand it as two waves ('A' 'B') meeting each other at that beamsplitter.
each wave will be split into two parts with one part trying to get through it, the other part will be reflected.
Already this is an entanglement, as both 'sides' of any one wave now are split into two.
So either you can see it as two Ions releasing photons, both getting entangled on their own,then mixed, meeting the detectors simultaneously.

Or, as they are coming from both sides simultaneously, you might see their waves as getting 'mixed' at that beamsplitter.
And here I get confused, when different waves meet they can reinforce each other.
Or they can quench each other but I don't see how they become 'entangled'?
But we will get two different 'half'-waves mixing into one 'whole' wave on both sides of the mirror.

Maybe one can see it as a 'entanglement'?
So let us assume that by meeting/splitting inside/outside the beamsplitter those two original waves now are 'entangled', or if you like interweaved/mixed.

That mean that the photons spin will be related when observed.
If one photon has what is called a 'spin up' when observed, the other photon must have a 'spin down' as I remember it. Here they use 'colours' to describe those possibility's.
As we have two times two possibilities from those Ions 'splitting' we should have either two, if seen as one 'whole' wave, where those two different 'half' waves now are 'mixed' or if seen as two entangled photons at each detector (from 'A' respective 'B')

As for the states of the Ions you only know at the beginning that they have an even probability to be in one of two states.
It is only when observed that this so called 'information' of any photon will 'fall out'
And as there is no 'information' defined when starting this experiment there is no way to know what 'state' of spin there might be before finally observing.

So I'm getting quite confused here?
They are saying that they are placing the Ion in a given 'groundstate' whatever that mean.
Then they state that the photons will reflect that 'groundstate'?
Or?

Then they give four possible colour combinations representing spin, polarization, or both?
I see it as two photons released from two Ions at the same time, getting split (entangled) each one by itself, and then 'mixed' together as two 'whole' waves, half from each Ion, again.

As I said, it made most sense when seen as waves, but then I'm not sure that mixing two already entangled 'waves' produces one entanglement afterwards?

But if they see it as two entanglements meeting a detector simultaneously?
then there would be four possibility's, right.

I don't get it to make sense.
Do you?

[Vern]

Hi yor_on; I think that the thing observed would be polarization in photons and maybe spin in the ions. I am with you in not understanding the whole concept of superposition. I know that it means an undetermined state, but don't see how it can mean all possible states at the same time. But that is QM theory; I don't see how it is proven.

Someone here recently pointed out that observations involve an event and an observer and that the two comprise a system. An observation for one such system does not guarantee that another such system with the same event but a different observer will agree on the outcome. It is difficult to fathom.

[swansont]

Superposition is being in two states at once using the description (basis) that you are using to describe your system.  It would be like using an XY coordinate system to describe the position of something that is normally only on either axis.  But you put the item on the line at 45º and now it's in both states at once.  (You could, however, use a different coordinate system to describe that particle: rotate your system by 45º and it's on an axis again).  In this case it looks to be a superposition of the "spin up" and "spin down" states for the electron.  And yes, it's confusing and made more so because it's a popular article summary of some pretty advanced QM.

The wording of the article linked to, saying that in most cases the photons cancel out and end up at the same detector, sounds like they are interfering, and that the interference is what entangles the photon states, and by extension, the ion states.

[yor_on]

Swansont:)

Yeah interference is definitively there, but if considered as waves I would expect that to be due to waves 'normal' interactions, quenching and strengthening.

But that mixing waves is 'entanglement'?
Do they transfer some magical property to mixing two already entangled waves.
Or is there a 'real' reason to why they call that result 'entangled'

To prove that this would be a real 'entanglement' they most certainly need to observe both detectors and observe that the spins are correct, don't you agree?

The idea, if correct, will allow us to create a 'network' of entanglements it seems to me?
And could we transfer information through that network we would have a 'direct' system communicating via one node to all nodes.

I could easily write a SF wherein this planet Erh have sent out entangled particles in such a 'net', all of them created as to be the same from one 'original' beamsplitter, for eons just waiting for us to observe their state and then having an instant communication:

Ahh;) Perhaps even sending it/them 'backwards' in time, hmm.
And if those concepts worked I would expect it to be already done too:)
As with monkeys and typewriters, there should be this possibility already 'materialized' in a expanding possibly 'infinite' universe.
Yes, I will need to get myself one of those new 'spin' readers:)


If the idea worked that is:)
I know that there is a definite difference between ftl and information flow.
And it make eminent sense to me.

It is 'spacetime' who define what works, not us.
To get to a state where FTL (including information transfer) would be possible we need either to get 'outside' of 'spacetime', but if so I'm not sure that we could get back in, as I have this feeling that there will be two problems to that. One to find our way out, and another to find our way in:)

Or we need to break what I see as 'spacetimes' symmetry.
But how to do that without creating enormous energy expenditure?

Maybe BEC:s are an answer, as we get a lot of strange effects out from that without expending to much energy though. As a BEC seems to be a way to break 'symmetry's', just as high energy particle research does.

[Vern]

Superposition is being in two states at once using the description (basis) that you are using to describe your system.  It would be like using an XY coordinate system to describe the position of something that is normally only on either axis.  But you put the item on the line at 45º and now it's in both states at once.  (You could, however, use a different coordinate system to describe that particle: rotate your system by 45º and it's on an axis again).

This is the most understandable description of superposition that I have ever seen. Thank you for your contribution.