Superconducting phase qubits with shadow-evaporated Josephson junctions

Su Fei-Fan^{1, 2}, Liu Wei-Yang^{1, 2}, Xu Hui-Kai^{1, 2}, Deng Hui¹, Li Zhi-Yuan^{1, 3}, Tian Ye¹, Zhu Xiao-Bo⁴, Zheng Dong-Ning¹, Lv Li¹, Zhao Shi-Ping^{1, 2, 5, †}

(color online) Energy spectroscopy of the fabricated phase qubit measured at 20 mK. Note that for the whole measurable qubit level spacing ranging from about 6 GHz to 8 GHz, no avoided crossing from coherent barrier TLS is seen. Inset shows the measured energy relaxation with at the qubit level spacing of 7.55 GHz.