Scalable 1.4 μW cryo-CMOS SP4T multiplexer operating at 10 mK for high-fidelity superconducting qubit measurements

In this work, we report on the electrical performance of an ultra-low-power cryo-CMOS single-pole-4-throw (SP4T) RF multiplexer working at 10 mK base temperature stage of a dilution refrigerator. We use the multiplexer to benchmark a superconducting qubit for the very first time and obtain qubit coherence times of over 35 μs along with an average single-qubit gate fidelity of 99.93%, which exceeds the threshold required for quantum error-correction based on surface-code. This work demonstrates the operability of superconducting qubits with ultra-low-power cryo-CMOS devices at the base temperature, paving the way for advanced co-integration schemes.