# Can three particles be entangled?

1. Feb 18, 2017

### caspeerrr

1. The problem statement, all variables and given/known data
I'm trying to understand the information paradox at a black hole. Can three particles be entangled? I read on a site that it's impossible to entangle multiple particles. When searching on google I found out that it is possible for multiple particles to entangle. So what

2. Relevant equations
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3. The attempt at a solution
I read on a site that it's impossible to entangle multiple particles. When searching on google I found out that it is possible for multiple particles to entangle. So is it or is it not possible for multiple particles to entangle and what are the concequences?
Thanks!

2. Feb 18, 2017

### Staff: Mentor

It is possible to entangle multiple particles, without limitation on their number. I don't know what you read where, it could have been related to the no-cloning theorem.

3. Feb 19, 2017

### Strilanc

You probably just misunderstood someone talking about monogamy of entanglement. If A is maximally entangled with B (i.e. they form an EPR pair) then neither can also be maximally entangled with C.

There are of course entangled states involving arbitrarily many particles, such as the GHZ state $\frac{1}{\sqrt 2}|000...0\rangle + \frac{1}{\sqrt 2}|111...1\rangle$ or the W state $\frac{1}{\sqrt n}|100..0\rangle+ \frac{1}{\sqrt n}|010..0\rangle + \frac{1}{\sqrt n}|001..0\rangle + ... + \frac{1}{\sqrt n}|000..1\rangle$, it's just that such states don't contain particles that are maximally entangled with each other.