  Controlled manipulation of quantum states is central to studying natural and
artificial quantum systems. If a quantum system consists of interacting
sub-units, the nature of the coupling may lead to quantum levels with
degenerate energy differences. This degeneracy makes frequency-selective
quantum operations impossible. For the prominent group of transversely coupled
two-level systems, i.e. qubits, we introduce a method to selectively suppress
one transition of a degenerate pair while coherently exciting the other,
effectively creating artificial selection rules. It requires driving two qubits
simultaneously with the same frequency and specified relative amplitude and
phase. We demonstrate our method on a pair of superconducting flux qubits. It
can directly be applied to the other superconducting qubits, and to any other
qubit type that allows for individual driving. Our results provide a
single-pulse controlled-NOT gate for the class of transversely coupled qubits.
