Photon-noise-tolerant dispersive readout of a superconducting qubit using a nonlinear Purcell filter

Abstract

Residual noise photons in a readout resonator become a major source of dephasing for a superconducting qubit when the resonator is optimized for a fast, high-fidelity dispersive readout. Here, we propose and demonstrate a nonlinear Purcell filter that suppresses such an undesirable dephasing process without sacrificing the readout performance. When a readout pulse is applied, the filter automatically reduces the effective linewidth of the readout resonator, increasing the sensitivity of the qubit to the input field. The noise tolerance of the device we have fabricated is shown to be enhanced by a factor of 3 relative to a device with a linear filter. The measurement rate is enhanced by another factor of 3 by utilizing the bifurcation of the nonlinear filter. A readout fidelity of 99.4% and a quantum nondemolition fidelity of 99.2% are achieved using a 40-ns readout pulse. The nonlinear Purcell filter will be an effective tool for realizing a fast, high-fidelity readout without compromising the coherence time of the qubit.

13 pages, 9 figures

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• Dissipative Quantum Chaos unveiled by Stochastic Quantum Trajectories
• Fault-tolerant quantum architectures based on erasure qubits
• Optimal control in large open quantum systems: the case of transmon readout and reset
• Efficient decoupling of a non-linear qubit mode from its environment
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• Parametric multi-element coupling architecture for coherent and dissipative control of superconducting qubits
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• Strongly driven cavity quantum electrodynamical-optomechanical hybrid system