Observation of high-order transitions in a transmon qubit coupled to coplanar waveguide cavity 張佑誠 ^{1,2*}, 陳則言^{1,2}, 王志洋^{1}, 管希聖^{2}, 陳啟東^{1}^{1}物理所, 中央研究院, 台北市, Taiwan^{2}物理所, 國立台灣大學, 台北市, Taiwan* presenting author:Yu-Cheng Chang, email:changyc@phys.sinica.edu.tw Coherent interaction between a transmon quantum bit and an on-chip superconducting cavity is studied. The transmon consists of a superconducting quantum interference device (SQUID), and the anharmonicity required for qubit operation is provided by the charging energy associated with the junction and the shunting interdigital structures. The transition frequency between the two lowest levels E01 of the transmon at zero magnetic field is about 6.414 GHz, and can be tuned continuously by the applied external magnetic flux threading the SQUID loop. As this level spacing is tuned to close to the resonance frequency of the Nb superconducting cavity (6.161 GHz), the Rabi-splitting feature emerges, indicating a coherence coupling between the qubit and the cavity. From the size of anti-crossing gap, the coupling strength is estimated to be 155MHz. In addition, the higher-order transitions E12, and E23 involving 2nd and 3rd excitation levels and multiple photons are observed, but there are no sign of qubit-cavity coupling.
Keywords: Qubit , Transmon, CPW cavity, Rabi-spliiting, SQUID |