[Geezer]

All seems pretty straightforward to me

Obviously, the entanglement has created a sort of super-particle. Even when you split it apart, it is still a super-particle.

This is a good way to think of it, Geezer.  In classical mechanics, we can always think of 2 particles as 2 separate particles that, if they interact, do so by forces.  In QM, entangled particles are actually 1 quantum state.  You can't separate them into 2 particles interacting via some force--somehow they are one "superparticle." 

I suppose why I'm saying you can remove the "magic" is that if you start from QM and accept that things like entanglement are part of nature, what becomes interesting is how these effects vanish as you go to large-scale (classical) objects.  A lot of confusion comes from starting with classical mechanics and trying to make sense of entanglement in terms of classical ideas--especially since it has no counterpart there.

I'm probably missing something here, but isn't this a very powerful argument to support the existence of other dimensions - as in String Theory? Are the famous double-slit photon experiments another indication?

[JP]

I'm missing something (not an unusual state for me to be in)--why would having two particles acting as one imply extra dimensions?

[rocking_1987 (OP)]

Sorry , I did not understand what you are trying to tell? Can you please bit explain it?

[yor_on]

When you have set the properties in a entangled system (half way mirror) both photons are entangled. To proof that you have a entanglement is difficult as a 'photon' by itself only exist in its 'creation', created by interacting with/in matter, and in its annihilation, which then becomes your measurement. As for the 'interference' I guess it depends on what will happen to those 'photons' as they move their separate ways after being split. I'm not fully sure myself what they mean by that as a photon either is 'there' and so able to be measured, or 'not there' which then presumably means that it has annihilated on the way (interacting with something). It may be they look at it as a 'wave' there, and that the 'wave' then changed on the way as in the idea of quantum cryptography . You need to read up on the wave/particle duality of light to see that one. But here is a very nice example of a entanglement. http://phys.org/news/2011-05-matter-matter-entanglement-distance.html

A BEC is a ultracold gas of atoms where all 'atoms vibrate' the absolute same, becoming as one 'super atom'. By sending in a 'photon' you can change the way it resonance, and then by interacting again with it (the BEC) using a laser make it send out a new photon of the exact same resonance/properties as that first 'photon' that was sent in 'tuning' the BEC.

So entanglements exist. Another even weirder idea is that you don't need to entangle those photons, electrons, atoms whatever. You just need to 'force' something (a photon, atom, etc) at A to behave the exact same as at B and then you have a same 'state' for them. It's called quantum discord.

"The degree of entanglement is often used as a figure of merit for determining its usefulness for quantum technologies. Strongly entangled systems, however, are very sensitive to extrinsic influence and difficult to prepare and to control. A team of researchers headed by the physicists Caslav Brukner (theory) and Philip Walther (experiment) at the University of Vienna have been able to show that in order to achieve successful remote state preparation entanglement is not the only way forward. Under certain circumstances, non-entangled states can outperform their entangled counterparts for such tasks - as long as they have a significant amount of so-called "quantum discord". This novel and not yet fully understood measure of quantum correlations quantifies the disturbance of correlated particles when being measured.

In their experiments, the researchers used a variety of two-photon states with different polarization correlations. "By measuring the polarization state of a certain photon we prepare the state of the respective partner photon remotely", explains Philip Walther. "In the experiment we observe how the quality of our remotely prepared quantum state is affected by changes in the quantum discord." This work provides an important and significant step towards future quantum information processing schemes that would rely on less demanding resources."  by a team of researchers headed by the physicists Caslav Brukner (theory) and Philip Walther (experiment) at the University of Vienna.