Enhanced pumping rate of artificial atoms coupled to a resonating mode

Weichen Chien^1*, Chien-Han Chen², Hiroshi Shimada³, Watson Kuo¹

¹Department of Physics, National Chung Hsing University, Taichung, Taiwan
²Institute of Physics, Academia Sinica, Taipei, Taiwan
³Department of Engineering Science, University of Electro-Communications, Tokyo, Japan

* Presenter:Weichen Chien, email:melcwc@gmail.com

In quantum computing, the coherence and relaxation times of qubits are relatively limited. As gate operation times increase, qubits become more susceptible to noise and decoherence, thereby raising the probability of gate operation errors and reducing computational accuracy. We employ a circuit-QED architecture, utilizing a main resonator at 5.378GHz for qubit state readout and an auxiliary mode at 6.682GHz to accelerate qubit excitation. We found that the qubit |g⟩-|e⟩ transition is enhanced when the auxiliary mode resonates with the |e⟩-|f⟩ transition, where |g⟩, |e⟩ and |f⟩ represents the ground, first, and second excited states, respectively. The populations of the 1st excited state (Pₑ) and the 2nd excited state (Pf) are determined by the transmission coefficient(T) of the readout microwave resonant with the main resonator, using the formulas P_e=((T-T_g ))⁄((T_e-T_g ) ) and P_f=((T-T_e ))⁄((T_f-T_e ) ). Here, Tg and T_e are the transmission coefficient when an excitation tone is applied at a frequency fo off-resonant and on-resonant to the |g⟩-|e⟩ transition with no pumping tone, respectively. As a strong pumping tone is applied resonant to |g⟩-|e⟩ transition, the qubit is excited to |e⟩ and Tf is the transmission coefficient when the excited tone is resonant with the |e⟩-|f⟩ transition. The ancillary mode, when resonant with the |e⟩-|f⟩ transition, enhances the |e⟩-|f⟩ pumping and the |g⟩-|e⟩ pumping efficiencies by a factor of 1.79 and 3, respectively. Furthermore, Autler-Townes splitting(ATS) in the|g⟩-|e⟩ transition is observed when the pump frequency is tuned to the |e⟩-|f⟩ transition. The ATS data also indicates 3-fold enhancement when the ancillary mode is in resonant with the |e⟩-|f⟩ transition. These findings demonstrate that resonantly coupling a mode to the |e⟩-|f⟩ transition significantly improves both |e⟩-|f⟩ and |g⟩-|e⟩ transition efficiencies, offering a promising pathway to improved qubit manipulation.

Keywords: Transmon, pumping enhancement, qubit