Yirong Jin

Observation of Bloch Oscillations and Wannier-Stark Localization on a Superconducting Processor

  1. Xue-Yi Guo,
  2. Zi-Yong Ge,
  3. Hekang Li,
  4. Zhan Wang,
  5. Yu-Ran Zhang,
  6. Peangtao Song,
  7. Zhongcheng Xiang,
  8. Xiaohui Song,
  9. Yirong Jin,
  10. Kai Xu,
  11. Dongning Zheng,
  12. and Heng Fan
In a crystal lattice system, a conduction electron can exhibit Bloch oscillations and Wannier-Stark localization (WSL) under a constant force, which has been observed in semiconductor
superlattice, photonic waveguide array and cold atom systems. Here, we experimentally investigate the Bloch oscillations on a 5-qubit superconducting processor. We simulate the electron movement with spin (or photon) propagation. We find, in the presence of a linear potential, the propagation of a single spin charge is constrained. It tends to oscillate near the neighborhood of initial positions, which is a strong signature of Bloch oscillations and WSL. In addition, we use the maximum probability that a spin charge can propagate from one boundary to another boundary to represent the WSL length, and it is verified that the localization length is inversely correlated to the potential gradient. Remarkably, benefiting from the precise simultaneous readout of the all qubits, we can also study the thermal transport of this system. The experimental results show that, similar to the spin charges, the thermal transport is also blocked under a linear potential. Our work demonstrates possibilities for further simulation and exploration of the Bloch oscillation phenomena and other quantum physics using multiqubit superconducting quantum processor.
arxiv pdf

High Quality Stepped-impedance Resonators suitable for Circuit-QED Measurement of Superconducting Artificial Atoms

  1. Yirong Jin,
  2. Hui Deng,
  3. Xueyi Guo,
  4. Yarui Zheng,
  5. Keqiang Huang,
  6. Luhui Ning,
  7. and Dongning Zheng
High quality factor coplanar resonators are critical elements in superconducting quantum circuits. We describe the design, fabrication and measurement of stepped impedance resonators
(SIRs), which have more compact size than commonly used uniform impedance resonators (UIRs). With properly chosen impedance ratio, SIRs can be much shorter in total length than that of UIRs. Two kinds of designs containing both SIRs and UIRs are fabricated and measured. The power dependence of the extracted internal quality factors (Qi) for all the resonators indicated that SIRs and UIRs had comparable performance at high incident power. However, as the incident power decreased, the internal quality factor of SIRs decreased much slower than that of UIRs. All the SIRs in design I kept near half-million Qi at single-photon level, while the two UIRs on the same chip decreased heavily to less than 2×105. These results indicate potential advantages of SIRs in quantum computer architectures: they consume less space than UIRs, while perform excellent under single-photon level. The resonators in design II were measured under a large residual magnetic field. The measured results showed that the internal quality factor of all the SIRs and UIRs were more or less suppressed. Such behavior confirmed that trapped vortices in the coplanar resonators provide another loss channel.
arxiv pdf