  Cryogenic qubit controllers (QCs) are the key to build large-scale
superconducting quantum processors. However, developing scalable QCs is
challenging because the cooling power of a dilution refrigerator is too small
(~10 $\mu$W at ~10 mK) to operate conventional logic families, such as
complementary metal-oxide-semiconductor logic and superconducting
single-flux-quantum logic, near qubits. Here we report on a scalable QC using
an ultra-low-power superconductor logic family, namely adiabatic
quantum-flux-parametron (AQFP) logic. The AQFP-based QC, referred to as the
AQFP-multiplexed QC (AQFP-mux QC), produces multi-tone microwave signals for
qubit control with an extremely small power dissipation of 81.8 pW per qubit.
Furthermore, the AQFP-mux QC adopts microwave multiplexing to reduce the number
of coaxial cables for operating the entire system. As a proof of concept, we
demonstrate an AQFP-mux QC chip that produces microwave signals at two output
ports through microwave multiplexing and demultiplexing. Experimental results
show an output power of approximately $-$80 dBm and on/off ratio of ~40 dB at
each output port. Basic mixing operation is also demonstrated by observing
sideband signals.
