Wei-Chen Chien

Dark state as a measurable state by a dispersive readout without a Purcell limit

  1. Wei-Chen Chien,
  2. Jyh-Yang Wang,
  3. Yen-Yu Chiang,
  4. Cheng-Chengh Huang,
  5. Lih-Chieh Hsaio,
  6. Yen-Chun Chen,
  7. Cen-Shawn Wu,
  8. Chiidong Chen,
  9. and Watson Kuo
It is believed that the enhancement in qubit-resonator coupling allows a better dispersive readout but introduces greater Purcell loss. In this work, we propose that a dark mode in
a coupled quantum system may violate this rule by introducing the ZZ interaction between the dark and a bright mode. The dark mode may exhibit an effective zero coupling strength, and zero Purcell loss with the resonator photons. Nevertheless, the dispersive shift is almost the same as the bright state, due to the higher order perturbation introduced by the higher excited states. Such a state demonstrates the measurability without a Purcell limit in circuit quantum electrodynamics.
arxiv pdf

Cavity quantum electrodynamics with dressed states of a superconducting artificial atom

  1. Yu-Han Chang,
  2. Dmytro Dubyna,
  3. Wei-Chen Chien,
  4. Chien-Han Chen,
  5. Cen-Shawn Wu,
  6. and Watson Kuo
We experimentally studied the microwave response of a transmon artificial atom coupled to two closely spaced resonant modes. When the atom is under driven with one of the modes, the
atom state and mode photons are superposed, forming the dressed states. Dressed states with 1st, 2nd and 3rd excited states of the atom were prepared and probed via the strong coupling to the other resonant mode from the point of view of cavity quantum electrodynamics. The transmission of the probe tone is modulated by the driving microwave amplitude, displaying multi-photon process associated with the inter-atomic level transitions. Our system provides an easy method to study the dressed states by driving one mode and probing the Landau-Zener transition of the other.
arxiv pdf