I was following the Qiskit textbook:
In this, there is a statement as indicated below:
With superconducting qubits, higher energy levels are also available, but we fabricate the systems to be anharmonic so that we can control which transition we are exciting. That way, we are able to isolate two energy levels and treat each qubit as a basic two-level system, ignoring higher energy states.
I understand that there are higher energy levels available, but how are we controlling which transition we are exciting by fabricating the system to be anharmonic?