Characterizing a custom-designed cryo-CMOS multiplexer with superconducting qubits

The integration of cryo-CMOS based control electronics in close proximity to qubits has significant advantages for large-scale superconducting quantum processors. However, the heat dissipation of such devices introduces additional thermal noise that affects the qubit performance. Experiments studying the impact of cryo-CMOS components on the behavior of superconducting qubits at millikelvin temperatures are currently lacking. Here, we explore the feasibility of including cryo-CMOS components near superconducting qubits by measuring a low-power custom-designed multiplexer operating at the base temperature of a dilution refrigerator. We characterize the noise properties of the multiplexer by configuring it as a passive thermal load to drive noise photons on the readout resonator of a qubit. By measuring the qubit's dephasing rate, we estimate the thermal noise power irradiated from the multiplexer. We show that with appropriate signal attenuation and thermalization, the qubit's performance is maintained. Our results demonstrate that properly optimized cryo-CMOS components placed at the base temperature of a dilution refrigerator can be used to reliably address multiple qubits, ultimately enabling large-scale quantum device characterization.