Dong-Ning Zheng

A superconducting qutrit link beyond the qubit limit

  1. Xiang Li,
  2. Zheng-Yang Mei,
  3. Yang He,
  4. Si-Lu Zhao,
  5. Yan-Jun Liu,
  6. Xiao-Hui Song,
  7. Kai Xu,
  8. Zhong-Cheng Xiang,
  9. Dong-Ning Zheng,
  10. and Heng Fan
Superconducting microwave links have enabled deterministic state transfer and remote entanglement between qubits, but deterministic links have so far operated with an effectively two-dimensional
transmitted Hilbert space. Here we demonstrate a superconducting qutrit link between two independently packaged nodes connected by a microwave channel. Each node combines a transmon qutrit, a transmission resonator, and a tunable Purcell-filter interface, allowing the two remote microwave-photon interfaces to be matched in both frequency and bandwidth. We implement two transition-selective photon-mediated operations that transfer the |e⟩ and |f⟩ qutrit components in distinct temporal modes of the same channel. We tomographically characterize arbitrary qutrit-state transfer, obtaining a mean transferred-state fidelity of 83.68% and a qutrit process fidelity of 77.12%, exceeding both the classical qutrit-transfer benchmark and the best possible average fidelity of an effective qubit channel used to transmit an arbitrary qutrit. Using partial-transfer operations, we reconstruct a remote two-qutrit state with negativity 0.730, a tomography-inferred dense-coding capacity of 2.273 bits, and a tomography-inferred Collins-Gisin-Linden-Massar-Popescu (CGLMP) parameter I3=2.332, all beyond the corresponding qubit or local bounds. These results demonstrate a superconducting microwave link that uses the native three-level structure of transmons as a genuine high-dimensional communication resource.
arxiv pdf

An efficient and compact quantum switch for quantum circuits

  1. Yulin Wu,
  2. Li-Ping Yang,
  3. Yarui Zheng,
  4. Hui Deng,
  5. Zhiguang Yan,
  6. Yanjun Zhao,
  7. Keqiang Huang,
  8. William J. Munro,
  9. Kae Nemoto,
  10. Dong-Ning Zheng,
  11. C. P. Sun,
  12. Yu-xi Liu,
  13. Xiaobo Zhu,
  14. and Li Lu
The engineering of quantum devices has reached the stage where we now have small scale quantum processors containing multiple interacting qubits within them. Simple quantum circuits
have been demonstrated and scaling up to larger numbers is underway. However as the number of qubits in these processors increases, it becomes challenging to implement switchable or tunable coherent coupling among them. The typical approach has been to detune each qubit from others or the quantum bus it connected to, but as the number of qubits increases this becomes problematic to achieve in practice due to frequency crowding issues. Here, we demonstrate that by applying a fast longitudinal control field to the target qubit, we can turn off its couplings to other qubits or buses (in principle on/off ratio higher than 100 dB). This has important implementations in superconducting circuits as it means we can keep the qubits at their optimal points, where the coherence properties are greatest, during coupling/decoupling processing. Our approach suggests a new way to control coupling among qubits and data buses that can be naturally scaled up to large quantum processors without the need for auxiliary circuits and yet be free of the frequency crowding problems.
arxiv pdf