Nb-based Josephson parametric amplifier for superconducting qubit measurement<xref rid="cpb_28_11_110303fn1" ref-type="fn">*</xref><fn id="cpb_28_11_110303fn1"><label>*</label><p>Project supported by the Science Funds from the Ministry of Science and Technology of China (Grant Nos. 2015CB921104 and 2016YFA0300601), the National Natural Science Foundation of China (Grant Nos. 11674380 and 11874063), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDB07010300 and XDB28000000), and the Key Research and Development Program of Guangdong Province, China (Grant No. 2018B030326001).</p></fn>

Nb-based Josephson parametric amplifier for superconducting qubit measurement**

Project supported by the Science Funds from the Ministry of Science and Technology of China (Grant Nos. 2015CB921104 and 2016YFA0300601), the National Natural Science Foundation of China (Grant Nos. 11674380 and 11874063), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDB07010300 and XDB28000000), and the Key Research and Development Program of Guangdong Province, China (Grant No. 2018B030326001).

Su Fei-Fan^{1, 2}, Wang Zi-Ting^{1, 2}, Xu Hui-Kai^{1, 2}, Zhao Shou-Kuan^{1, 2}, Yan Hai-Sheng^{1, 2}, Yang Zhao-Hua^{1, 2}, Tian Ye^{1, 2}, Zhao Shi-Ping^{1, 2, 3, †}

Inphase-quadrature and histogram plots of the single-shot measurement of an Xmon qubit prepared in the |0〉 (blue) and |1〉 (red) states, performed with the pump of the IMPA off (a), (b) and on (c), (d). The horizontal axes in panels (b) and (d) are defined along the directions from the center of the |1〉 state cloud to that of the |0〉 state cloud in panels (a) and (c). Qubit |0〉 and |1〉 states measurement fidelities are above 97% and 91%, respectively.