Microwave Engineering Challenges in Readout of Superconducting Qubits

Designing readout circuits for superconducting qubits is an exercise in constrained optimization. At the schematic level, frequency crowding, heat load, qubit performance, and speed trade off against each other. However, fundamental improvements in amplifiers, impedance matching, losses, or multiplexing would alleviate these constraints to varying degrees, so the field is ripe for contributions from the microwave community. To enable those contributions, this talk describes the basic principles of qubit readout via dispersed microwave pulses and analyzes the constraints that govern readout designs. We show how improvements in losses, impedance matching, and non-reciprocal device design stand to enable the next-generation devices.