Modulation of energy spectrum and control of coherent microwave transmission at single-photon level by longitudinal field in a superconducting quantum circuit*

Project supported by the Ministry of Science and Technology of China (Grant Nos. 2014CB921401, 2017YFA0304300, 2014CB921202, and 2016YFA0300601), the National Natural Science Foundation of China (Grant No. 11674376), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB07010300).
Guo Xueyi1, 2, Deng Hui1, Li Hekang1, 2, Song Pengtao1, 2, Wang Zhan1, 2, Su Luhong1, 2, Li Jie1, Jin Yirong1, †, Zheng Dongning1, 2, ‡
       

(color online) (a) Optical micrograph of the Xmon qubit of the first sample. The green part is a λ/4 CPW resonator for readout. The red cross part is the capacitor of Xmon and the inset shows the DC-SQUID of Xmon which works as an adjustable non-linear inductance. The XY control line is used to apply a transverse field drive and the Z control line is used to apply the bias field and thus to apply LFM. (b) Schematic diagram of measurement setup. (c) Energy spectra of the Xmon qubit measured as a function of bias voltages. (d) Xmon qubit energy spectra variation with LFM amplitude. The qubit is biased at Φ = 0.15758Φ0, corresponding to an energy difference ω0 = 6.1455 GHz and the LFM frequency is fixed at 20 MHz. (e) Resonate peak intensity as a function of LFM amplitude for 6 branches (corresponding to n = 0, −1, …, −5) shown in (d). The solid lines are fitting of the Bessel function (Eq. (5)) to the experimental data.