Fast multiplexed superconducting qubit readout with high assignment fidelity

In superconducting quantum circuits, measurement constitutes a major component of the error budget and execution time for algorithms requiring detection and feedback. This talk will focus on achieving fast and high-fidelity qubit readout using the dispersive interaction between the qubit and a readout resonator. We show how the readout resonator can be coupled capacitively and inductively to a filter resonator in order to produce a compact Purcell-filter circuit that effectively eliminates the Purcell energy-relaxation channel of the qubit. The design is readily implemented into a 3D-integrated circuit architecture with four-to-one multiplexed readout developed by our team. By designing large readout mode linewidths up to 42 MHz, we achieve 56-ns simultaneous readout of four qubits, with the qubit assignment fidelities ranging from 99.65% to 99.91%. We introduce pulse schemes to benchmark measurement-induced state transitions, and demonstrate that fast, high-fidelity dispersive readout can be achieved without causing significant leakage out of the computational basis.