Dapeng Yu

Spin wave based tunable switch between superconducting flux qubits

  1. Shaojie Yuan,
  2. Chuanpu Liu,
  3. Jilei Chen,
  4. Song Liu,
  5. Jin Lan,
  6. Haiming Yu,
  7. Jiansheng Wu,
  8. Fei Yan,
  9. Man-Hong Yung,
  10. Jiang Xiao,
  11. Liang Jiang,
  12. and Dapeng Yu
Quantum computing hardware has received world-wide attention and made considerable progress recently. YIG thin film have spin wave (magnon) modes with low dissipation and reliable control
for quantum information processing. However, the coherent coupling between a quantum device and YIG thin film has yet been demonstrated. Here, we propose a scheme to achieve strong coupling between superconducting flux qubits and magnon modes in YIG thin film. Unlike the direct Nāˆ’āˆ’āˆš enhancement factor in coupling to the Kittel mode or other spin ensembles, with N the total number of spins, an additional spatial dependent phase factor needs to be considered when the qubits are magnetically coupled with the magnon modes of finite wavelength. To avoid undesirable cancelation of coupling caused by the symmetrical boundary condition, a CoFeB thin layer is added to one side of the YIG thin film to break the symmetry. Our numerical simulation demonstrates avoided crossing and coherent transfer of quantum information between the flux qubits and the standing spin waves in YIG thin films. We show that the YIG thin film can be used as a tunable switch between two flux qubits, which have modified shape with small direct inductive coupling between them. Our results manifest that it is possible to couple flux qubits while suppressing undesirable cross-talk.
arxiv pdf

Simulation of Higher-Order Topological Phases and Related Topological Phase Transitions in a Superconducting Qubit

  1. Jingjing Niu,
  2. Tongxing Yan,
  3. Yuxuan Zhou,
  4. Ziyu Tao,
  5. Xiaole Li,
  6. Weiyang Liu,
  7. Libo Zhang,
  8. Song Liu,
  9. Zhongbo Yan,
  10. Yuanzhen Chen,
  11. and Dapeng Yu
Higher-order topological insulators (TIs) and superconductors (TSCs) give rise to new bulk and boundary physics, as well as new classes of topological phase transitions. While higher-order
TIs have been actively studied on many platforms, the experimental study of higher-order TSCs has thus far been greatly hindered due to the scarcity of material realizations. To advance the study of higher-order TSCs, in this work we carry out the simulation of a two-dimensional spinless second-order TSC belonging to the symmetry class D in a superconducting qubit. Owing to the great flexibility and controllability of the quantum simulator, we observe the realization of higher-order topology directly through the measurement of the pseudo-spin texture in momentum space of the bulk for the first time, in sharp contrast to previous experiments based on the detection of gapless boundary modes in real space. Also through the measurement of the evolution of pseudo-spin texture with parameters, we further observe novel topological phase transitions from the second-order TSC to the trivial superconductor, as well as to the first-order TSC with nonzero Chern number. Our work sheds new light on the study of higher-order topological phases and topological phase transitions.
arxiv pdf