Coherent Interaction between Superconducting Qubits and Photons in Circuit Quantum Electrodynamics
Jyh-Yang Wang1*, Yu-Cheng Chang1, Ze-Yan Chen1, Teik-Hui Lee1, Cen-Shawn Wu2, Watson Kuo3, Chii-Dong Chen1
1Institute of Physics, Academia Sinica, Taipei, Taiwan
2Department of Physics, National Chang-Hua University of Education, Changhua, Taiwan
3Department of Physics, National Chung Hsing University, Taichung, Taiwan
* presenting author:Jyh-Yang Wang,
Coherent interaction between two superconducting transmon qubits and an on-chip microwave cavity is studied. Each transmon consists a flux-tuned Josephson junction and a shunting multi-finger capacitor, which is for reducing the effective charging energy of the transmon so as to suppress the noise induced by the charge fluctuation. Our microwave cavity is a half-wavelength coplanar waveguide made of Nb with resonance frequency of 5.96GHz. With no flux bias, the transition frequencies of each transmon are 10.1GHz and 9.3GHz respectively. They can be tuned to meet the cavity resonance frequency by increasing the flux bias. In our experiment, anti-crossing features appear at qubit-cavity zero detuning points, showing the coherent interaction between qubits and the cavity. By fitting the anti-crossing features around the cavity resonance with the Jaynse-Cummings model, the qubit-cavity coupling strengths of the two transmons are estimated to be 165MHz and 160MHz, respectively. According to this information, we also located the qubit-qubit zero detuning points, where another anti-crossing features are shown. They are corresponding to the entanglement of the two transmons due to the effective qubit-qubit interaction.

Keywords: qubit, Circuit QED