Quantum Entanglement

[5614]

No. Any interaction breaks the entanglement

ok i understand the first bit of your answer (that makes sense - not quoted).

 

however the quoted part - what is the "entanglement bond"? we talk about it, but is it the thing which makes the total spin zero? it if is only that, then when it is broken, presumably one of the atoms could change its spin if it wanted? but then entaglement wouldnt work, so it must keep the previously 'given' values.

 

then what is it in the first place that makes the atoms 'mirror' each others spin... or is THAT the wierdness of entaglement?

[RICHARDBATTY]

I don't want to change or damage this thread and what I have previously put forward is only my opinion, but if you look at the theory of space time and movement again and fully understand it allbeit with an open mind it explains entanglement and the weirdness barrier. Please continue to post in this thread I only wish to offer a possible explanation.

[swansont]

The reason the system has zero spin is because you chose the system, and prepared it in an entangled way. Spin is a form of angular momentum, and it's conserved in an isolated system. If you prepare two spin 1/2 particles so that they have zero total spin, one of them will be +1/2 and the other will be -1/2. (aka up and down)

 

The "bond" is the fact that QM is non-local. Einstein's "spooky action at a distance"

[5614]

yeah yeah, but what im trying to say is well, you have two particles that are their original spin, how do you make one go up and one go down?

like how do you force the properties upon an atom?

 

once you set one, pressumably the other one changes automatically? although you wouldnt know because if you measure it the bond is broken...

but theoretically you could keep changing one and the other would keep changing... not that you'd know because you cant meansure it, but in theory would that happen?

[1veedo]

No no no, you're missing it completely.

 

Lets say that I have two cards, a king and a queen. Now lets say that I flip them over and randomly put both cards into separate boxes. We have no idea what card is where. We open box A to find the king. This means that box B has the queen. If the queen would have ben found in box A then box B would hold the king.

[TheProphet]

yeah yeah' date=' but what im trying to say is well, you have two particles that are their original spin, how do you make one go up and one go down?

like how do you force the properties upon an atom?

 

once you set one, pressumably the other one changes automatically? although you wouldnt know because if you measure it the bond is broken...

but theoretically you could keep changing one and the other would keep changing... not that you'd know because you cant meansure it, but in theory would that happen?[/quote']

 

Nopes, in QM these to are undetermined until you measure them.. and once you measure one of them! The Entagnlement are destroyed.! So all you have is a 50/50 chance of getting spin upp or down!

[swansont]

yeah yeah' date=' but what im trying to say is well, you have two particles that are their original spin, how do you make one go up and one go down?

like how do you force the properties upon an atom?[/quote']

 

The total spin is a property of the particle (e.g. spin 1/2) but the orientation (up or down) is not. So if you have two spin 1/2 particles and prepare them so the toal is 0, you must have one spin up and one down.

 

once you set one' date=' pressumably the other one changes automatically? although you wouldnt know because if you measure it the bond is broken...

but theoretically you could keep changing one and the other would keep changing... not that you'd know because you cant meansure it, but in theory would that happen?[/quote']

 

No. Once you change one particle's spin, the entanglement is broken.

[NSX]

I'm a bit lost from step 3 --> 4. How is the result of the measurement sent to ion C? Or is that the nature of entanglement?

The measurement result can be sent any way you want - digital signal along an optical fiber; carrier pigeon. It's because this communication is necessary that means that no information exceeds c. The entanglement is the "tie" between the two original particles.

 

 

I still don't understand this part.

 

So ... does ion B call ion C on it's new cell phone and say: "hey, I've been detected as +1/2 now, you've got change to -1/2 now" ?

[swansont]

 

I still don't understand this part.

 

So ... does ion B call ion C on it's new cell phone and say: "hey' date=' I've been detected as +1/2 now, you've got change to -1/2 now" ?[/quote']

 

ion C isn't entangled. You prepare it based on the state you've detected for ion A or B.

[5614]

The total spin is a property of the particle (e.g. spin 1/2) but the orientation (up or down) is not. So if you have two spin 1/2 particles and prepare them so the toal is 0, you must have one spin up and one down.

thats the bit which is confusing... how do you say "you must have an up spin and you must have a down"? what if you happen to chose to up atoms?

how do you make one go in the opposite direction spin to the other?

[TheProphet]

thats the bit which is confusing... how do you say "you must have an up spin and you must have a down"? what if you happen to chose to up atoms?

how do you make one go in the opposite direction spin to the other?

 

If the Particles are truly entangeled what u say here won't happen.

[5614]

if that is so then what if by chance you happen to have two particles which are both up spin, then how can they have a total of 0 spin and how can you KNOW for certain what the other one is?

[swansont]

if that is so then what if by chance you happen to have two particles which are both up spin, then how can they have a total of 0 spin and how can you KNOW for certain what the other one is?

 

They can't. Two spin up particles won't have a total spin of 0.

 

 

You start with a neutral pion, which is spin 0. It decays into an electron and a positron, which are both spin 1/2. In order for angular momentum to be conserved, one must be spin up, and the other spin down. There's no other option.

[5614]

"Two spin up particles won't have a total spin of 0."

you think?? yeah obviously!

 

"You start with a neutral pion, which is spin 0. It decays into an electron and a positron, which are both spin 1/2. In order for angular momentum to be conserved, one must be spin up, and the other spin down"

ok, that makes sense with the decay --> 1/2 up and 1/2 down to conserve angular momentum...

the decay of the electron/positron would make the atoms ions

ok but then you have a electron/positron which are mirroring each others spin, but that does not make the ions (was atoms) mirror each others spin... but i thought that you could get the whole ion to mirror each other.

 

i say mirror each other because you are meant to be able to measure one atom and know the spin of the other, but i cant see how you imply the whole spin thing upon the whole atom.

 

also, once the entaglement process has happened and the atoms are mirroring each other, then surely there is no disadvantage of breaking the 'bond', as once they are mirroring each other they wouldnt really change of their spin of their own accord!? so theres no advantage in keeping the bond????

[TheProphet]

5614: After a Pion decays it produces an Electron - Positron pair. Which in turn are entagnled in the decay! There are no ions (positiv or negatic atoms, which u already know) or for that instance atoms involved in the process swansont describes! Just a Pion. Whom is an elementeray particle, and should not be in any way related to atoms ions.. A Pion decays in a e- and p+.

[swansont]

also, once the entaglement process has happened and the atoms are mirroring each other, then surely there is no disadvantage of breaking the 'bond', as once they are mirroring each other they wouldnt really change of their spin of their own accord!? so theres no advantage in keeping the bond????

 

Since you don't know which one is spin up or down, if you interact with one without measuring the spin (e.g. you put it in a field that forces it to be spin up no matter what) then the information is lost, along with the entanglement. So yes, there is an advantage to keeping the bond.

 

(And to anticipate, for everyone's sake, the common misunderstanding that comes along: No, forcing one to be spin up does not force the other one to be spin down. The interaction breaks the entanglement)

[5614]

ok so you have two random atoms floating around, you decide to entagle them.

 

obviously one will have up spin and one down, obviously you dont know which is which until you measure it, my question:

 

The reason the system has zero spin is because you chose the system, and prepared it in an entangled way. Spin is a form of angular momentum, and it's conserved in an isolated system. If you prepare two spin 1/2 particles so that they have zero total spin, one of them will be +1/2 and the other will be -1/2. (aka up and down)

i dont 100% understand this quote. do all atoms have +1/2 or -1/2 spin? i think so. can one individual atom have 0 spin? i dont think so... whatever the answer, sometimes you will have to vary the spin of one of the atoms to make it 'fit into' the entaglement (pressumably because the atoms are chosen at random, you could have two up spin atoms, so one would have to go down), so when you say "prepared it in an entangled way" how does this work? how can you prepare them in such a way that it will over-ride their original spin properties?

[swansont]

i dont 100% understand this quote. do all atoms have +1/2 or -1/2 spin? i think so. can one individual atom have 0 spin? i dont think so... whatever the answer, sometimes you will have to vary the spin of one of the atoms to make it 'fit into' the entaglement (pressumably because the atoms are chosen at random, you could have two up spin atoms, so one would have to go down), so when you say "prepared it in an entangled way"[/i'] how does this work? how can you prepare them in such a way that it will over-ride their original spin properties?

 

No. Fermi particles have half-integral spin. These are the particles that obey the Pauli exclusion principle. The spin can be 1/2, 3/2, etc. You can have nuclei, atoms, or individual subatomic particles ( like electrons, neutrons and protons - all are spin 1/2). Nuclei with an odd number of nucleons (spin-1/2) will have half-integral spin. But depending on the structure, you can get larger values - Cs-133, for example, has nuclear spin 7/2.

 

You also have Bosons, which have integral spin. 0, 1, 2... Mesons are spin 0. Nuclei with an even number of nucleons will have integral spin.

 

Rb-87 has 87 nucleons, and the nucleus has spin 3/2. But the atom itself, because it has 37 electrons (i.e. an odd number), has an integral spin.

 

You can't choose the spin of the atom. You can only choose the orientation (i.e. the direction the angular momentum vector points)

[5614]

You can't choose the spin of the atom. You can only choose the orientation (i.e. the direction the angular momentum vector points)

but surely choosing the directions of the angular momentum's vector points is the same (effectively) as choosing the spin... in that is would come out with the same results.

 

also, doing that would still (by probability - sometimes) involve changing the spin from its original spin...

 

so how can you force the atom to change spin.... or how can you choose the orientation of the atom?... basically how can you change the atoms spin and force those properties apon that atom?

[swansont]

but surely choosing the directions of the angular momentum's vector points is the same (effectively) as choosing the spin... in that is would come out with the same results.

 

also' date=' doing that would still (by probability - sometimes) involve changing the spin from its original spin...

 

so how can you force the atom to change spin.... or how can you choose the orientation of the atom?... basically how can you change the atoms spin and force those properties apon that atom?[/quote']

 

In the nomenclature the spin is the magnitude of spin, projected along the z axis. That value is fixed for particles. The direction of the vector can be changed, but only from one projection (up) to the other (down). It's quantized.

 

here's a discussion of some of the details of the Stern-Gerlach experiment

[5614]

The direction of the vector can be changed, but only from one projection (up) to the other (down).

 

what im trying to find out is how you can just take any old atom and force a certain spin onto it?

 

maybe to help me understand you could explain HOW you would carry out this process?

[swansont]

what im trying to find out is how you can just take any old atom and force a certain spin onto it?

 

You can't. Spin is inherent to the system. All you can do is change the orientation. That will depend on, and be measured in reference to, an external magnetic field. But the magnitude of the spin is fixed.

[5614]

ok, so how would one go about entagling two atoms?

[swansont]

ok, so how would one go about entagling two atoms?

 

For spin1/2 atoms, one way would be to confine them in a potential well, and cool them into the ground state. Since they are fermions, they would have to be of opposite spin orientation.