Towards large-scale superconducting-qubit readout enabled by millikelvin electronics

For conventional high-fidelity readout of superconducting qubits, microwave signals are delivered to the qubit from room-temperature electronics through careful attenuation and filtering to the cryogenic environment, and the output signal is typically amplified at the millikelvin stage using parametric amplifiers. The consequent hardware overhead will limit further scaling of quantum processors in the future. Recently, nano-bolometers have been demonstrated to provide single-shot dispersive readout of superconducting qubits without parametric amplifier, and coherent cryogenic microwave signal sources have been reported to generate microwave emission at millikelvin temperatures. These novel devices feature small footprint, reduced passive heat load and full compatibility with superconducting quantum circuits, providing an appealing substitute for millikelvin parametric amplifiers and room temperature electronics. In this talk, I will discuss a scheme of monolithic integration of microwave sources and thermal detectors with the qubits at millikelvin. This integrated readout architecture greatly reduces the hardware overhead, and provides a relief to the heat and size limitations in the fridge, thus introducing a promising approach towards persistent scaling of superconducting quantum processors.