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

Question

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 $$frac{1}{sqrt{2}}(|00rangle+e^{itheta}|11rangle)$$
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.

Mariia Mykhailova · Answer

Apply a CNOT gate with one of the qubits as control and the other as target. You'll get

$$frac{1}{sqrt{2}}(|0rangle+e^{itheta}|1rangle) otimes |0rangle$$

Use the methodology from How to get the relative phase of a qubit? for the first qubit :-)

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

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