I am trying to use Qiskit to write a code that uses QFT to add 2 numbers. I am referring to this paper: https://iopscience.iop.org/article/10.1088/1742-6596/735/1/012083
I have a few questions: 1) Is the $R$ rotation gate in this paper equivalent to the Controlled-U1 gate in Qiskit?
2) Why does the value of $k$ change?
3) The program is supposed to add $1$ and $2$. Number $1$ is encoded as $01$, represented by the zero vector $(1,0)$ and the 1 vector $(0,1)$. When does number $2$ come into play? It seems that they keep performing operations on number $1$ until the end.
4) Number $1$ is represented by $0$ on $a_1$ and $1$ on $a_2$. And number $2$ consists of $1$ on $b_1$ and $0$ on $b_2$, is that right?