Post-fabrication resonator frequency trimming enabling fast, high-fidelity dispersive readout of transmon qubits

Fast, high-fidelity dispersive readout in circuit QED that does not impact qubit relaxation can be achieved using a dedicated Purcell-filter resonator coupled to the readout resonator. Optimal conditions are achieved when the bare frequencies of both resonators are accurately matched so that they form a hybridized system. This requirement can be challenging to meet in fabrication due to non-uniformity of the base layer thickness and previously untested design changes, among other reasons. We present a practical method allowing accurate trimming of the bare frequency of either resonator as gleaned necessary from initial device characterisation. We compare the speed of photon depletion before and after trimming and demonstrate the enhancement of readout fidelity and speed without impacting qubit relaxation. The method does not require extra fabrication steps and also allows the elimination of any frequency collisions between resonators used to measure different qubits with a common feedline.