I would like to know how the gates are defined in quantum random access codes? Consider the $2 \to 1$ code described in Lemma 3.1 of this paper.
The section defines the encoding and decoding circuits. But it is not clear to me how to define gates. Say, I want to apply an $Rz(\theta)$ on the first qubit or a CNOT gate on both qubits.
How do I do that?