Directional emission of a readout resonator for qubit measurement

Robust and scalable multiplexed qubit readout is essential for realizing a fault-tolerant quantum computer. Conventional approaches rely on intentional mismatch of the feedline to provide directionality to the readout signal, at the cost of increased variation in resonator linewidth, which ultimately degrades quantum error correction. The authors address this challenge by demonstrating high-fidelity qubit readout using a readout resonator that emits photons preferentially toward the output, across its full bandwidth. By maintaining directional decay of the readout signal without intentional mismatch, this work presents a path toward the design of reliable, modular quantum processors.