  A challenge for scaling up quantum processors using frequency-crowded, weakly
anharmonic qubits is to drive individual qubits without causing leakage into
non-computational levels of the others, while also minimizing the number of
control lines. To address this, we implement single-qubit Wah-Wah control in a
circuit QED processor with a single feedline for all transmon qubits, operating
at the maximum gate speed achievable given the frequency crowding. Randomized
benchmarking and quantum process tomography confirm alternating qubit control
with $\leq$1% average error per computational step and decoherence-limited
idling of one qubit while driving another with a Wah-Wah pulse train.
