Prep_y

By default, all qubits are initialized in the $|0 \rangle$ state. With the prep_y instruction, qubits will be initialized in the y-basis in the $\vert R\rangle =\frac{\vert 0 \rangle + \imath \vert 1 \rangle}{\sqrt{2}}$ state:

State initialization can be done at the beginning of an algorithm, but it can also be done during an algorithm (re-initialization). Be aware that re-initialization of a qubit will also reset the binary register entry for that qubit to zero.