【量子光学】 Quantum Optics 2 Quiz 5.1(13)

Quantum Optics 2课程第十三次测验

第1题 (单选)

In the Ekert protocol presented in the video 5.1, the key is generated by selecting situations where Alice and Bob have performed measurements along the same directions, i.e., $\alpha = \beta$.
How to adapt this protocol if the source produces entangled photons in the state $\left|\Phi^-\right\rangle=\frac{1}{\sqrt{2}}(\left|x_1,x_2\right\rangle-\left|y_1,y_2\right\rangle)$ instead of $\left| \Phi^{+} \right\rangle$ ?

A) The exact same protocol can be used.

B) The key can be generated by keeping the same situations where $\alpha=\beta$, but by inverting the bit of Bob such that $\left|+_b\right\rangle$ corresponds to 0 and $\left|-_b\right\rangle$ to 1.

C) The key can be generated by selecting situations where the orientations of the polarizers fulfil $\alpha =- \beta$.

D) The protocol cannot be adapted in the case of photons in the state $\left| \Phi^{-} \right\rangle$.

第2题 (单选)

Which Bell state could be used for quantum key distribution using the same protocol than the one in the video but inverting the bits of Bob?

A) $\left| \Phi^{-} \right\rangle$

B) $\left| \Psi^{+} \right\rangle$

C) $\left| \Psi^{-} \right\rangle$

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