Tie-Fu Li

Method for identifying electromagnetically induced transparency in a tunable circuit quantum electrodynamics system

  1. Qi-Chun Liu,
  2. Tie-Fu Li,
  3. Xiao-Qing Luo,
  4. Hu Zhao,
  5. Wei Xiong,
  6. Ying-Shan Zhang,
  7. Zhen Chen,
  8. J. S. Liu,
  9. Wei Chen,
  10. Franco Nori,
  11. J. S. Tsai,
  12. and J. Q. You
Electromagnetically induced transparency (EIT) has been realized in atomic systems, but fulfilling the EIT conditions for artificial atoms made from superconducting circuits is a more
difficult task. Here we report an experimental observation of the EIT in a tunable three-dimensional transmon by probing the cavity transmission. To fulfill the EIT conditions, we tune the transmon to adjust its damping rates by utilizing the effect of the cavity on the transmon states. From the experimental observations, we clearly identify the EIT and Autler-Townes splitting (ATS) regimes as well as the transition regime in between. Also, the experimental data demonstrate that the threshold ΩAIC determined by the Akaike information criterion can describe the EIT-ATS transition better than the threshold ΩEIT given by the EIT theory.
arxiv pdf

Four-junction superconducting circuit in both flux and phase regimes

  1. Yueyin Qiu,
  2. Wei Xiong,
  3. Xiao-Ling He,
  4. Tie-Fu Li,
  5. and J. Q. You
We develop a theory for the quantum circuit consisting of a superconducting loop interrupted by four Josephson junctions and pierced by a magnetic flux (either static or time-dependent).
In addition to the similarity with the typical three-junction flux qubit, we demonstrate the difference of the four-junction circuit from its three-junction analogue, especially its distinct advantages over the latter. Moreover, the four-junction circuit in the phase regime is also investigated. Our theory provides a tool to explore the physical properties of this four-junction superconducting circuit.
arxiv pdf

A hybrid quantum circuit consisting of a superconducting flux qubit coupled to both a spin ensemble and a transmission-line resonator

  1. Ze-Liang Xiang,
  2. Xin-You Lu,
  3. Tie-Fu Li,
  4. J. Q. You,
  5. and Franco Nori
We propose an experimentally realizable hybrid quantum circuit for achieving a strong coupling between a spin ensemble and a transmission-line resonator via a superconducting flux qubit
used as a data bus. The resulting coupling can be used to transfer quantum information between the spin ensemble and the resonator. More importantly, in contrast to the direct coupling without a data bus, our approach requires far less spins to achieve a strong coupling between the spin ensemble and the resonator (e.g., 3 to 4 orders of magnitude less). This drastic reduction of the number of spins in the ensemble can greatly improve the quantum coherence of the spin ensemble. This proposed hybrid quantum circuit could enable a long-time quantum memory when storing information in the spin ensemble.
arxiv pdf