Can you entangle more than two particles? Can entanglement be produced on a macroscopic scale to observe new physical interactions?

Submitted by and-no-and-then t3_1233e8a in askscience

Particle entanglement is often described as spooky action at a distance. Where two particles interact regardless of the physical distance between them. Entanglement has also been described as a measurement of one particle that decides the properties of another because the interaction between them determines their shared properties that must be conserved. However, can the entanglement include more particles, can this be expanded to a macroscopic level to observe things like additional dimensions or new physics?

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mfb- t1_jdu3qaz wrote

In principle you can entangle as many particles as you want. A prominent example is the GHZ state. You can also get entanglement with effective particles like phonons where you could say the entanglement includes the whole object.

The more particles you include the harder it tends to get to preserve entanglement.

> Where two particles interact regardless of the physical distance between them.

They don't interact with each other.

> can this be expanded [...] to observe things like additional dimensions or new physics?

No.

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the_fungible_man t1_jdu7skt wrote

I read the article you linked, and achieved 0% comprehension, which made me wonder, how esoteric is the information it presented? Pretty basic for physics post-grad students? Or only those with advanced degrees specifically in more narrow physics specialties?

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mfb- t1_jdu8hgd wrote

The state itself should be easy to understand after a course on quantum mechanics, so hopefully for most with a BSc in physics. The state is a superposition of these two options "all particles are in state 1" and "all particles are in state 0" (for some systems that have these two options for each particle). It's pretty similar to the typical example of two entangled particles where you have one particle in one state and the other in the other, or both in the same state. Just with a third particle.

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Blakut t1_jduspez wrote

so there is no |101> state?

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El_Sephiroth t1_jdzq8h1 wrote

More like |-1,0,1> because |101> would be |0>+2×|1> If I remember correctly

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Mikesturant t1_jdu7w7c wrote

How many entangled particle groups can function independently of each other while still grouped.

If that makes sense.

Can you have multiple entanglements of different data in the same grouping or proximity

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mfb- t1_jdu8nfp wrote

What do you mean by "function independently"?

> Can you have multiple entanglements of different data in the same grouping or proximity

Yes.

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Mikesturant t1_jdu9fe5 wrote

Nice. Like a fiber optic trunk cable. In essence.

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Fenrisvitnir t1_jduev91 wrote

>How many entangled particle groups can function independently of each other while still grouped.

Not sure what you mean here - you can in theory cross-entangle entangled groups of particles, but I doubt that is what you are really asking.

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Mikesturant t1_jduf5j1 wrote

I'm also not sure how to ask.

The entanglement is data or information? Yes?

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dyrin t1_jdv1pgi wrote

Entanglement is data/information about the state of the particle at the moment of entanglement.

But they can't transfer any information after the entangled particles have been seperated.

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Mikesturant t1_jdvon9w wrote

Isn't this the same as the Stanford lady and moving the light particles through empty space?

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Fenrisvitnir t1_jdvvdm9 wrote

Entanglement is a constraint on information about the particles. ie. if one was spin up, the other must be spin down, but we don't know which is which.

Let me ask this question - are you thinking about sending information over optical fiber using paired photons? Entangled photons can't send information, there must always be a classical information pathway for networking applications.

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Mikesturant t1_jdvvqj3 wrote

No the optical fiber remark was a comparison.

As a not physicist I'm wondering if the entanglement is being used with the condensate method of capturing photons and reproducing them in another space.

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Blakut t1_jdusvyv wrote

afaik one can't even tell if two specific particles are entangled just by measuring them.

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mfb- t1_jdv9ey7 wrote

For two particles you can't be sure, indeed, you can only tell from statistics if you have a large sample.

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Fenrisvitnir t1_jduel01 wrote

>Where two particles interact regardless of the physical distance between them.

Technically this is wrong - the two particles are pair-linked by state no matter the distance between them. They don't send information back and forth. We don't know the mechanism for preserving the entanglement.

>Entanglement has also been described as a measurement of one particle that decides the properties of another because the interaction between them determines their shared properties that must be conserved.

This is closer because at the most fundamental level is when two particles are entangled, the shared state constraints between them are preserved until measurement of either or both (and possibly after). But the measurement simultaneously collapses the state of both particles, potentially even when done to the original system state before the particles left it. However, again, we don't know the underlying mechanism (is it non-local binding? pilot waves? collapse of probabilities?).

The wrong way to think about entanglement is a pair of particles that send info back and forth between them to make sure everything checks out - they share state, they don't exchange it. This is why parallel worlds, pilot waves, etc. are theories about how the state is shared are more accurate because they attempt to preserve the state constraints globally. Nothing about entanglement moves faster than the speed of light.

And to answer your question, yes, entanglement does appear to be transitive to other particles under the right conditions, so you can chain state constraints.

This assumes that entanglement is correctly understood by experiment today, which is still not entirely clear, even though the physics community has settled on Copenhagen for the most part.

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DragonZnork t1_jdud88p wrote

Yes, you can entangle more than two particles or qubits, it has been done many times already. However, it becomes increasingly difficult with higher numbers of objects. Entangling particles or qubits "by hand" up to macroscopic scales is unlikely, at least for now because it's a huge number of things.

On the other hand, superconductivity is an entangled state in some sense, and definitely reaches macroscopic scales.

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Boredgeouis t1_jdzontl wrote

I'll only say a few sentences on this because it's rather high level, but in strongly interacting condensed matter systems something called 'topological order' can occur. The ground state of a many body system (ie a macroscopic one) can have long range entanglement, such that every particle is entangles together. These systems can have some weird emergent properties, like Fractional Qiantum Hall Effect; simplifying quite a lot, in this the particles behave as in they have fractions of an electron charge.

For these systems the interesting thing isnt necessarily learning about their existing interactions (after all it's just electrons and electromagnetism) but what weird emergent properties are visible. Systems like this have some potential applications in Quantum Computing: this talk https://m.youtube.com/watch?v=smX2lSyi2js explains a little.

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Movpasd t1_je6g1l2 wrote

You can entangle as many particles as you want -- however, there is a property of quantum entanglement called the monogamy of entanglement. This could be interpreted as a limit on the extent to which systems of many particles can be inter-entangled.

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