I Maximally entangled two-qubit Bell states

[kaje]

Hello,
In the four maximally entangled two-qubit Bell states, what is the difference between the first and the second states, similarly, the difference between the third and the fourth states. What the different in signs mean( +,-)
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[DrClaude]

Please do not use svg images. Do they not come out correctly.

I can anyway answer your question. You will notice that $\Psi^\pm$ and $\Phi^\pm$ differ by the sign between the two terms. This change of sign ensures orthogonality.

 

[kaje]

Thank you..

For instance, in phi state for both (+ and -), in the first term Alice would get 0 and Bob 0 as well for both (+,-). Actually, it is not clear in terms of definition and the way of measurement, as both look similar.

Thanks.