Bell States

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The generalized Bell States are defined as

$\begin{matrix} |\Psi^{\pm}\rangle&=&(|1_A 0_B\rangle\pm |0_A 1_B\rangle)/\sqrt{2}\\ |\Phi^{\pm}\rangle&=&(|1_A 1_B\rangle\pm |0_A 0_B\rangle)/\sqrt{2} \end{matrix}$

for a partition ${A, B}$ . If the subsystem $A$ has more than one spin, $1 A$ is interpreted as $1_1 \cdots 1_{N_A}$ and similarly for $1 B$ , $0 A$ , and $0 B$ .