Atomic Entanglement: Could Macro Objects Become Entangled?

[Thenewdeal38]

http://physicsworld.com/cws/article/news/31068

I thought only elctrons could be entangled but now atoms and even ions can be entangled. Would this suggest that it could work its way to the macro levels. Could two diffrent rocks or soccer balls become entangled?

 

[DrChinese]

You can entangle a lot of different subatomic and atomic particles. And you can entangle more than 2. Keep in mind that the rules for the possible outcomes vary substantially in these cases. So even if you entangled macro-sized objects, that would not mean that you could see the collapse of their states or similar.

 

[Thenewdeal38]

I thought for objects to be entangled they have to be exactly the same structuraly.

 

[ZapperZ]

I thought for objects to be entangled they have to be exactly the same structuraly.

Since you've found the Physics World website, maybe you should do an even deeper search on many of these topics that would have answered your question. For example, you might have missed these:

http://physicsworld.com/cws/article/print/19417
http://physicsworld.com/cws/article/news/24099

Those would have addressed your question above.

Zz.

 

[xts]

I thought for objects to be entangled they have to be exactly the same structuraly.

Not necessirilly, although it is most common, as it is easiest experimentally.

You must remember that those are not 'particles' entangled, but their 'properties'. You may have (actually - that's a case of most of photon entangled experiments) photons having entangled spins (polarisation), but their other properties (momentum, energy, position) are not entangled. Photons are so simple, that you may create a pair of them entangled regarding all their properties (spins, momentum/position, energy). But in case of more complex structures, like ions, atoms, etc. - if you read about 'entangled ions', entanglement refer only to single property (e.g. excitement state, or spin)

 

[DrChinese]

I thought for objects to be entangled they have to be exactly the same structuraly.

Nope. They normally follow a conservation rule. Example: total spin=0, total momentum=x, total charge=y, etc.

Because of the ease of creation, identification, and handling, entangled photon pairs created by PDC are most commonly used for entanglement studies. But that is simply a practical consideration.

If you take a free neutron, it will decay into a proton and an electron (plus a bit more which I ignore for this example) in an average of about 15 minutes. The proton and electron will be entangled as to spin and momentum.

 

[Thenewdeal38]

So can macro objects become entangled or are there limitations?

 

[DrChinese]

There are some practical limitations on the size of entangled objects, as you might guess. First, you need a conserved observable. Then you need a way to test the entanglement. Because of the large number of eigenstates those objects could have, this becomes exponentially difficult.

 

[Thenewdeal38]

First, you need a conserved observable. Then you need a way to test the entanglement. Because of the large number of eigenstates those objects could have, this becomes exponentially difficult.

Scuese my ignorance, but a conserved observable is? Also what logisticlly is it about the number of eigenstates that limits an objects probability of entangling?

 

[xts]

If you take a free neutron, it will decay into a proton and an electron (plus a bit more which I ignore for this example) in an average of about 15 minutes. The proton and electron will be entangled as to spin and momentum.

You can't ignore this little brother - they won't be!
The whole triplet of proton, electron and antineutrino will be triple entangled.
Especially regarding spin - proton and electron won't be correlated at all (if you analyse them ignoring antineutrino), as antineutrino tooks -1/2 or +1/2 with equal probabilities.

 

[Thenewdeal38]

Wait don't you entangle things by splitting a bigger thing in two? I know what a hillbilley way to ask a question.

 

[xts]

Wait don't you entangle things by splitting a bigger thing in two? I know what a hillbilley way to ask a question.

That's the easiest way, but you may entangle their properties (not them!) on many other ways, e.g. scattering one particle on another, or causing any kind of interaction between two particles such, that some property is preserved (e.g. momentum - due to conservation principle), but which may be exchanged between particles during interaction in an unpredictable way.

 

[Thenewdeal38]

Wait is quantum entanglemt instentanous or just faster than the speed of light?

 

[DrChinese]

You can't ignore this little brother - they won't be!
The whole triplet of proton, electron and antineutrino will be triple entangled.
Especially regarding spin - proton and electron won't be correlated at all (if you analyse them ignoring antineutrino), as antineutrino tooks -1/2 or +1/2 with equal probabilities.

Of course you are correct about them, I was simply trying to give a simplified example. Although I oversimplified, since (anti)neutrino spin can be + or - and therefore there are more permutations to consider for spin.

At any rate, the whole example should show Thenewdeal38 how complex things can get quickly. This is just for a neutron. Imagine 2 (magically) entangled molecules, and how many states they could be in, and how you would attempt to observe experimentally the state for one alone (which would collapse the other).

 

[DrChinese]

Wait is quantum entanglemt instentanous or just faster than the speed of light?

An interesting article appeared yesterday essentially indicating that collapse cannot occur at a finite speed (or else FTL signaling would be possible).

http://arxiv.org/abs/1110.3795

"The experimental violation of Bell inequalities using spacelike separated measurements precludes the explanation of quantum correlations through causal influences propagating at subluminal speed. Yet, it is always possible, in principle, to explain such experimental violations through models based on hidden influences propagating at a finite speed v>c, provided v is large enough. Here, we show that for any finite speed v>c, such models predict correlations that can be exploited for faster-than-light communication. This superluminal communication does not require access to any hidden physical quantities, but only the manipulation of measurement devices at the level of our present-day description of quantum experiments. Hence, assuming the impossibility of using quantum non-locality for superluminal communication, we exclude any possible explanation of quantum correlations in term of finite-speed influences. "

 

[Thenewdeal38]

Wait as objects get bigger is it harder for them to entangle or is it harder to measure their entanglment or probably both. But what speccificly make it harder for bigger objects to entangle?

 

[xts]

I see I must repeat: entanglement is not an objective property of a single object (so you could not say: Mickey is entangled, but Minnie is not) - it is a measure of correlations which may be possibly found between the particle and its "entangled twin" (or entangled siblings - possibly many). Neither Mickey nor Minnie wear their entanglement rings. You must analyse them both to find they were entangled. And it may occur they were entangled regarding some property, but not entangled regarding other properties.
Actually, except of trivial cases (Bertleman's socks) you can't even tell that a pair of particles were entangled. You may found mysterious statistical correlations only if you analyse multiple pairs.

Bigger the object is, more difficult is to measure it precisely enough to find those correlations and more difficult is to protect it from getting into entanglement with yet more other objects. Correlations may be found only analysing all entangled siblings (forgive me some simplification here, e.g. regarding total energy)
It is pretty easy to protect a photon from flipping its spin, and extremely difficult to protect a fulerene from being displaced by 2pm.
But, of course, in idealistic platonic world of QM thought experiments, it is even you who are getting entangled with a photon just because you spotted its twin with your eye!