We call $\hat{P}_{\vec{u}}=\left|\vec{u}\right\rangle\left\langle\vec{u}\right|$ the projector associated to the eigenvalue +1 of a measurement with polarizer along the $\vec{u}$ axis. How can be expressed the quantum observable $\hat{A}$ associated to a measurement of the polarization of photon $\nu_1$ along $\vec{x}$?
第2题 (不定项选择)
Just after a measurement of the polarization of photon $\nu_1$ yielding +1, what is the quantum state $\left|\psi_M\right\rangle$ of the pair of photons initially in the state $\left|\psi\right\rangle$?
第3题 (单选)
Considering a pair of photons in the EPR state $\left|\psi_{EPR}\right\rangle=\frac{1}{\sqrt{2}}(\left|x_1, x_2\right\rangle+\left|y_1, y_2\right\rangle)$, what is the quantum state $\left|\psi_M\right\rangle$ after this measurement?