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

Understand

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.