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, †}

Reflected phase of the low-power signal versus the dc flux bias I_b and signal frequency ω_s/2π. The periodic structure can be seen with clear borders (zero phase) across which the reflected phase changes from plus to minus, or vice versa.