Multiplexed superconducting qubit control at millikelvin temperatures with a low-power cryo-CMOS multiplexer

Large-scale superconducting quantum computers require the high-fidelity control and readout of large numbers of qubits at millikelvin temperatures, resulting in a massive input–output bottleneck. Cryo-electronics based on complementary metal–oxide–semiconductor technology could provide a scalable and versatile solution. However, detrimental effects due to cross-coupling between the qubits and the electronic and thermal noise generated during cryo-electronics operation need to be avoided. Here we report a low-power radio-frequency multiplexing cryo-electronics system that operates below 15 mK with a minimal cross-coupling. We benchmark its performance by interfacing the system with a superconducting qubit and observe that the qubit’s relaxation times are unaffected, whereas the coherence times are marginally affected in both static and dynamic operations. Using the multiplexer, single-qubit gate fidelities above 99.9%—that is, above the threshold for surface-code-based quantum error correction—can be achieved with appropriate thermal filtering. We also demonstrate time-division multiplexing capabilities by dynamically windowing calibrated qubit control pulses.