# How to access/ read $\alpha$ and $\beta$ values of a certain qubit in a multi-qubit system in a for loop?

In order to rotate the qubit state I need first to be able to read the values of $$\alpha$$ and $$\beta$$ and based on their values I will apply the Q-Gate for rotating the states of the single Qubits in the multi-qubit system I have.

Does anyone have an idea how to read these values?.

Using an Aer simulator reads the angles but only once, while I need to read and manipulate the states in a for loop so the simulator gives me the following error in the second run of the loop:

QiskitError: 'You have to select a circuit or schedule when there is more than one available'

• Getting the values for $\alpha$ and $\beta$ in $\alpha|0\rangle + \beta|1\rangle$ (up to some arbitrary precision) requires quantum state tomography, which needs a large amount of copies of the state you want the amplitude of. Sep 3, 2021 at 10:51
• While @epelaaez answer seems right in principle, based on your QiskitError, the problem may just be that you are trying to access a single circuit in an array of circuits. Would you be able to post a link to the code ? Sep 3, 2021 at 12:17