High-performance multiplexed readout of superconducting qubits with a tunable broadband Purcell filter
Phys. Rev. Applied 25, 054010 – Published 5 May, 2026
DOI: https://doi.org/10.1103/ykvq-bkfk
Abstract
Fast, high-fidelity, and low-backaction readout plays a crucial role in the advancement of quantum error correction (QEC). Here we demonstrate high-performance multiplexed readout of superconducting qubits using a tunable broadband Purcell filter, effectively resolving the fundamental trade-off between measurement speed and photon noise–induced dephasing. By dynamically tuning the filter parameters, we suppress photon noise–induced dephasing by a factor of 7 in idle status, while enabling rapid, high-fidelity readout during measurement. Using 100 ns readout pulses, we achieve low crosstalk simultaneous readout of three qubits with a relaxation-limited average fidelity of 99.5%. By using a multilevel readout technique, we overcome the relaxation constraint and achieve a fidelity of 99.9% with a 50 ns readout pulse. The system also exhibits high-performance quantum-nondemolition characteristics, maintaining 99.4% fidelity over repeated measurements with a qubit state leakage rate below 0.1%. Building on the tunable filter, we further propose a scalable readout scheme for surface code implementation with enhanced multiplexing capability, providing a promising pathway toward fast and scalable QEC.
