= Bell-state nondemolition measurement
{c}
{title2=$P_{z,x}=\frac14(I+zZ_AZ_B)(I+xX_AX_B)$}
The <Bell states> are joint <eigenstates> of commuting $Z_AZ_B$ and $X_AX_B$. Two shared <Bell state> meter pairs realize their two <entanglement-assisted nondemolition parity measurements> using spacelike local circuits. Their projector products give the four rank-one <Bell state> outcomes and preserve each input <Bell state>. The globally identified outcome requires later <local operations and classical communication>.
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