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 second sample. The green part is a one-dimensional open transmission line. The red part is the Xmon and the inset is the dc-SQUID of Xmon. LFM can be applied through Z control line. (b) Schematic diagram of experiment setup for transmission spectrum measurement. The incident microwave is fed in through port 1 and the output signal is picked up on port 2. LFM is generated by an AWG and the dc bias is generated by a dc voltage source. These two bias signals are combined by a bias-tee and connect to the Z control line. (c) Transmission coefficient S21 as a function of incident microwave power at the frequency in resonant with the Xmon qubit. In this case, the frequency is 6.42793 GHz. The red dot is the experiment data, and the blue solid line is the fitting curve of Eq. (??). (d) Qubit energy spectra variation with dc bias obtained from S21 measurements without LFM. (e) Qubit energy spectra at a fixed dc-bias, corresponding to a qubit frequency 5.779 GHz, measured from S21 measurements with LFM. The LFM frequency is 50 MHz and the amplitude is varied.