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## Main Question or Discussion Point

In book Quantum computing explained by David Mahon concurrence, as a measure of entanglement is defined as

[tex]C(\psi)=|\langle \psi|\tilde{\psi} \rangle |[/tex]

where ##|\psi\rangle=Y \otimes Y|\psi^*\rangle##

or with density matrix

##\rho(Y \otimes Y)\rho^{\dagger}(Y \otimes Y)##.

Could someone explain me what is ##|\tilde{\psi}\rangle## and ##Y##?

[tex]C(\psi)=|\langle \psi|\tilde{\psi} \rangle |[/tex]

where ##|\psi\rangle=Y \otimes Y|\psi^*\rangle##

or with density matrix

##\rho(Y \otimes Y)\rho^{\dagger}(Y \otimes Y)##.

Could someone explain me what is ##|\tilde{\psi}\rangle## and ##Y##?