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

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 undesired 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 fabricated is shown to be enhanced by a factor of three relative to a device with a linear filter. The measurement rate is enhanced by another factor of three by utilizing the bifurcation of the nonlinear filter. A readout fidelity of 99.4% and a QND 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.Comment: 13 pages, 9 figure

Light microscopy images of hematoxylin–eosin-stained transverse sections of the left (A) and right (B) cervical sympathetic ganglia at 6 months after ethanol injection.

<p>While the left side exhibited no ganglion cells in the entire ganglion, the right side exhibited ganglion cells throughout the ganglion. Scale bars, 50 μm.</p

Electrophysiological findings in the IAN at 3 months after surgery.

<p>Electrophysiological findings in the IAN at 3 months after surgery.</p

Percent changes in oral mucosal blood flow in the left mental region after cervical sympathetic ganglion block (CSGB).

<p>Blood flow was measured in the region dominated by the left mental arterial branch. The proportion of oral mucosal blood flow on the left side after CSGB remained significantly higher than that at baseline for up to 7 weeks. Values are expressed as mean ± standard deviation; *P < 0.01 in comparison with the baseline value.</p

Semi-thin transverse sections (A–C; toluidine blue staining) and transmission electron microscopy images (D–F) of the regenerated inferior alveolar nerve (IAN) at 3 months post-reconstruction.

<p>Distal segments of the regenerated left IAN in the reconstruction-only (A, D) and reconstruction + cervical sympathetic ganglion block (reconstruction+CSGB; B, E) groups. (C, F) Central segment of the right IAN in the reconstruction-only group (normal control). Black and white arrowheads indicate myelinated and non-myelinated nerve fibers, respectively. Scale bars, 50 μm (A–C) and 5 μm (D–F).</p

Changes in average nasal skin temperature after left cervical sympathetic ganglion block (CSGB).

<p>There was a significant increase in average nasal skin temperature after CSGB, which lasted for 10 weeks on the left side and 3 weeks on the right side. Values are expressed as mean ± SD. *P < 0.01 in comparison with the baseline value.</p