We have seen that in order to have a qubit in a quantum dot 2 magnetic fields are needed. One of these is perpendicular to the plane (applied magnetic field), whereas the other one is on it (alternating magnetic field). Can you tell why each of them is needed?
A constant magnetic field perpendicular to the plane is needed to have a splitting of the energy levels. This way each spin belongs to a different quantum state and qubits can be encoded. It is important that this magnetic field is constant and perpendicular to the plane.
On the other hand, an alternating magnetic field is needed in order to control the qubits. This needs to be on the plane because it must be perpendicular to the other magnetic field. We have seen that the frequency of the wave needs to match the resonance frequency of the qubit.