Rearranging equation in Dirac-notation for 3 particles (quantumteleportation)

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SUMMARY

The discussion focuses on rearranging a quantum state in Dirac notation for three particles, specifically in the context of quantum teleportation as outlined in Nielsen's textbook on quantum computation. The initial state is given as |p⟩ = (1/2)[a(|0⟩ + |1⟩)(|00⟩ + |11⟩) + b(|0⟩ - |1⟩)(|10⟩ + |01⟩)], which participants aim to rearrange into a different form. The confusion arises from the incorrect assumption that |00⟩|1⟩ and |1⟩|00⟩ are equivalent, which leads to a misunderstanding of the state expansion. The correct approach involves recognizing the distinct states represented in the tensor product.

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keen23
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Hello all!
I try to follow the computation in my textbook (nielsen, quantum computation) and miss a step.

Homework Statement


They say the following state
[tex]|p\rangle=\frac{1}{2}\big[a (|0\rangle+|1\rangle)(|00\rangle+|11\rangle)+b(|0\rangle-|1\rangle)(|10\rangle+|01\rangle)\big][/tex]
could be rearranged to
[tex]|p\rangle=\frac{1}{2}\big[|00\rangle(a|0\rangle+b |1\rangle)+|01\rangle(a|1\rangle+b|0\rangle)+|10\rangle(a|0\rangle-b|1\rangle)+|11\rangle(a|1\rangle-b|0\rangle)}\big][/tex].

But I don't see how.

(The start state comes from combining an arbitrary state a|0>+b|1> with an epr-pair in bell-state, then using CNOT for particles 1 and 2, then Hadamardgate on particle 1, well, I think that's not important for my question).

Homework Equations



The Attempt at a Solution


With normal expansion I get:
[tex]|p\rangle=\frac{1}{2}\big[a|0\rangle|00\rangle+a|0\rangle|11\rangle+a|1\rangle|00\rangle+a|1\rangle|11\rangle+b|0\rangle|10\rangle+b|0\rangle|01\rangle-b|1\rangle|10\rangle-b|1\rangle|01\rangle[/tex]
[tex] =|00\rangle a(|0\rangle +|1\rangle )+|01\rangle b(|0\rangle -|1\rangle )+|10\rangle b(|0\rangle -|1\rangle )+|11\rangle a(|0\rangle +|1\rangle )[/tex]

So "normal" expansion seems not to be the right way, but how shall I do it? Even if I think about the physical meaning I don't see what's wrong.
Maybe someone has more experience?
Thanks for your help!
 
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I think your mistake is that you're setting |00>|1> and |1>|00> equal -- but surely the first one equals |001> and the second equals |100>, which are different?
 
Oh no! Yes, sure. that was my mistake.
Thank you!
 

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