  Control electronics for superconducting quantum processors have strict
requirements for accurate command of the sensitive quantum states of their
qubits. Hinging on the purity of ultra-phase-stable oscillators to upconvert
very-low-noise baseband pulses, conventional control systems can become
prohibitively complex and expensive when scaling to larger quantum devices,
especially as high sampling rates become desirable for fine-grained pulse
shaping. Few-GHz radio-frequency digital-to-analog converters (RF DACs) present
a more economical avenue for high-fidelity control while simultaneously
providing greater command over the spectrum of the synthesized signal. Modern
RF DACs with extra-wide bandwidths are able to directly synthesize tones above
their sampling rates, thereby keeping the system clock rate at a level
compatible with modern digital logic systems while still being able to generate
high-frequency pulses with arbitrary profiles. We have incorporated custom
superconducting qubit control logic into off-the-shelf hardware capable of
low-noise pulse synthesis up to 7.5 GHz using an RF DAC clocked at 5 GHz. Our
approach enables highly linear and stable microwave synthesis over a wide
bandwidth, giving rise to high-resolution control and a reduced number of
required signal sources per qubit. We characterize the performance of the
hardware using a five-transmon superconducting device and demonstrate
consistently reduced two-qubit gate error (as low as 1.8%) which we show
results from superior control chain linearity compared to traditional
configurations. The exceptional flexibility and stability further establish a
foundation for scalable quantum control beyond intermediate-scale devices.
