# How to get the relative phase of an entangled pair of qubits

I have an extension to the following question: How to get the relative phase of a qubit? How do I get the relative phase of a pair of entangled qubits such as $$\frac{1}{\sqrt{2}}(|00\rangle+e^{i\theta}|11\rangle)$$

in which I want to find theta. I tried to use a similar methodology as the answer in the linked question above, but with no success.

• In the thread that was mentioned in the question, there was a mistake in this answer, that is corrected now. Jul 27 '20 at 11:27

$$\frac{1}{\sqrt{2}}(|0\rangle+e^{i\theta}|1\rangle) \otimes |0\rangle$$
• Shouldn't it be the state after CNOT $\frac{1}{\sqrt{2}}(|0\rangle + e^{i\theta}|1\rangle)\otimes |0\rangle$? Jul 22 '20 at 6:49