I dont understand why info cant be sent with entangled tripletes

[antonio glez]

all right so alice has one atom of the entangled triplet and bob the other two atoms

bob is going to always measure in horizontal basis

so alice sends a message by measuring in the horizontal basis or vertical

when bob measures always in the horizontal basis he will know in what basis did alice measure by having two equals or two differents values in the tripletes

why is this wrong?

 

[zonde]

It's hard to understand how do you imagine triplet entanglement.
If you imagine entanglement of two particles as two identical particles then it may seem that nothing prevents having three identical copies of particle. But such picture would be wrong as entanglement is more complex correlation of some property of particles from ensemble and their phase.

Anyways it's not enough to know measurement basis for particles to observe some correlations. You have to know results of measurements. That is true for triplet states as well.

 

[S.Daedalus]

If you have two maximally entangled qubits, they can't be entangled at all with a third one; this is known as http://www.quantiki.org/wiki/Monogamy_of_entanglement" . If the statistics on particles A and B violate a Bell inequality, those for A and C don't.

 

[dkotschessaa]

My understanding is that it doesn't matter what we measure, the outcome of that measurement is beyond our control. Since we can't control the outcome we can't communicate information in this way. Now I haven't heard this discussed with triplets as I've never heard of such a thing.

 

[antonio glez]

"If you have two maximally entangled qubits, they can't be entangled at all with a third one"

then what sense does it make talk of an entangled triplet?

 

[antonio glez]

so if a cuantum pair has an entanglement of 100% an entangle triplet has an entagle of 50%

is that correct?

 

[antonio glez]

also even taking into account quantum monogamy i still see posible to send info with a triplet

we agree that if the triplet is 100% entangled the receiver who has rwo atoms can know with a 100% efectivity in what basis did the sender measure

but if the triplet is entangled in a 50% the receiver will have a 50% chance of obtaining different values in his two atoms of the triplet if he measures in different basis

but a 50% chance of 50% of obtaining equal values if he measures in the same basis

so with triplets seems you can send a bit if not with a 100% certainty with more than 50%, the bit would be weather the sender measure in vertical or horizontal basis

any light on this?

 

[DrChinese]

You can have entanglement of 3 or more particles. However, this does not produce expectation statistics identical to 2 particles.

 

[Lievo]

why is this wrong?

I'm not an expert but from layman to layman here is how I understand this question:

Let's say we're talking about the spin of three electrons in the following state : [000> + [111> (vertical basis)

If Alice measures the first electron first, then the state own by Bob will be either [00> or [11>. One of the two, but he won't know which one.

Let's say Alice measures the first electron in an orthogonal basis, then to see what happens we need to rewrite the state of the first electron in this new basis

( [+> + [-> ) . [00> + ( [+> - [-> ) . [11>
<=> [+> . ( [00> + [11> ) + [-> . ( [00> - [11> )

If Alice measures the state of her electron she will see either [+> or [-> and the state own by Bob will be either [00> + [11> or [00> - [11>.

So it turns out that Bob will always see his two electrons agreeing. What he can measure is not affected by Alice, and that's why there is no communication.

 

[antonio glez]

"So it turns out that Bob will always see his two electrons agreeing."

thats the crux of what i see probably wrong:

if he sees the electrons agreeing he knows both alice and bob measured in the same basis contrary to if they had mesaured in different basis

then the message would be 0 horizontal 1 vertical

 

[Lievo]

thats the crux of what i see probably wrong

Yep. If Bob choses the vertical axis he will see two 0 or two 1. If he choses the horizontal avis he will see two + or two -. If he choses one vertical and one horizontal axis he will see any combination of 0 or 1 and + or -. That is not affected by what Alice does.

The only thing that can happen is that if Alice and Bob meet again, and they happened to have chosen the same basis, they will constat that they got the same result, whatever the result they had. But no way to send information, or at least not this way.
PS: I replaced ( that would violate the no-cloning theorem.) in the last sentence: I'm not sure of that.

 

[antonio glez]

i see so when alice measures his particle the entanglement is not broken but the other two atoms that bob have keep entangled so he will measure the same values always

is this correct?

 

[Lievo]

Yes

 

[antonio glez]

thanks a lot seems now i can agree with the thing :)