Yulong Liu

Near-ground state cooling in electromechanics using measurement-based feedback and Josephson parametric amplifier

  1. Ewa Rej,
  2. Richa Cutting,
  3. Debopam Datta,
  4. Nils Tiencken,
  5. Joonas Govenius,
  6. Visa Vesterinen,
  7. Yulong Liu,
  8. and Mika A. Sillanpää
Feedback-based control of nano- and micromechanical resonators can enable the study of macroscopic quantum phenomena and also sensitive force measurements. Here, we demonstrate the
feedback cooling of a low-loss and high-stress macroscopic SiN membrane resonator close to its quantum ground state. We use the microwave optomechanical platform, where the resonator is coupled to a microwave cavity. The experiment utilizes a Josephson travelling wave parametric amplifier, which is nearly quantum-limited in added noise, and is important to mitigate resonator heating due to system noise in the feedback loop. We reach a thermal phonon number as low as 1.6, which is limited primarily by microwave-induced heating. We also discuss the sideband asymmetry observed when a weak microwave tone for independent readout is applied in addition to other tones used for the cooling. The asymmetry can be qualitatively attributed to the quantum-mechanical imbalance between emission and absorption. However, we find that the observed asymmetry is only partially due to this quantum effect. In specific situations, the asymmetry is fully dominated by a cavity Kerr effect under multitone irradiation.
arxiv pdf

Gatemon qubit based on a thin InAs-Al hybrid nanowire

  1. Jierong Huo,
  2. Zezhou Xia,
  3. Zonglin Li,
  4. Shan Zhang,
  5. Yuqing Wang,
  6. Dong Pan,
  7. Qichun Liu,
  8. Yulong Liu,
  9. Zhichuan Wang,
  10. Yichun Gao,
  11. Jianhua Zhao,
  12. Tiefu Li,
  13. Jianghua Ying,
  14. Runan Shang,
  15. and Hao Zhang
We study a gate-tunable superconducting qubit (gatemon) based on a thin InAs-Al hybrid nanowire. Using a gate voltage to control its Josephson energy, the gatemon can reach the strong
coupling regime to a microwave cavity. In the dispersive regime, we extract the energy relaxation time T1∼0.56 μs and the dephasing time T∗2∼0.38 μs. Since thin InAs-Al nanowires can have fewer or single sub-band occupation and recent transport experiment shows the existence of nearly quantized zero-bias conductance peaks, our result holds relevancy for detecting Majorana zero modes in thin InAs-Al nanowires using circuit quantum electrodynamics.
arxiv pdf