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.

Charge-SQUID and Tunable Phase-slip Flux Qubit

  1. Hu Zhao,
  2. Tiefu Li,
  3. Jianshe Liu,
  4. Wei Chen,
  5. and J. Q. You
A phase-slip flux qubit, exactly dual to a charge qubit, is composed of a superconducting loop interrupted by a phase-slip junction. Here we propose a tunable phase-slip flux qubit
by replacing the phase-slip junction with a charge-related superconducting quantum interference device (SQUID) consisting of two phase-slip junctions connected in series with a superconducting island. This charge-SQUID acts as an effective phase-slip junction controlled by the applied gate voltage and can be used to tune the energy-level splitting of the qubit. Also, we show that a large inductance inserted in the loop can reduce the inductance energy and consequently suppress the dominating flux noise of the phase-slip flux qubit. This enhanced phase-slip flux qubit is exactly dual to a transmon qubit.