Broadband bandpass Purcell filter for circuit quantum electrodynamics

In circuit quantum electrodynamics, qubits are typically measured using dispersively coupled readout resonators. Coupling between each resonator and its electrical environment, however, reduces the qubit lifetime via Purcell effect. Inserting a filter counters this effect while maintaining high fidelity but measurement bandwidth and, thus, limits multiplexing capacity. Letter, we develop implement multi-stage bandpass that yields better protection simultaneously increasing multiplexed We report on experimental performance of our transmission-line-based implementation approach, flexible design can easily be integrated with current scaled-up, long coherence time superconducting processors.