J. Han

A tunable coupler for suppressing adjacent superconducting qubit coupling

  1. X. Li,
  2. T. Cai,
  3. H. Yan,
  4. Z. Wang,
  5. X. Pan,
  6. Y. Ma,
  7. W. Cai,
  8. J. Han,
  9. Z. Hua,
  10. X. Han,
  11. Y. Wu,
  12. H. Zhang,
  13. H. Wang,
  14. Yipu Song,
  15. Luming Duan,
  16. and Luyan Sun
Controllable interaction between superconducting qubits is desirable for large-scale quantum computation and simulation. Here, based on a theoretical proposal by Yan et al. [Phys. Rev.
Appl. 10, 054061 (2018)] we experimentally demonstrate a simply-designed and flux-controlled tunable coupler with continuous tunability by adjusting the coupler frequency, which can completely turn off adjacent superconducting qubit coupling. Utilizing the tunable interaction between two qubits via the coupler, we implement a controlled-phase (CZ) gate by tuning one qubit frequency into and out of the usual operating point while dynamically keeping the qubit-qubit coupling off. This scheme not only efficiently suppresses the leakage out of the computational subspace but also allows for the acquired two-qubit phase being geometric at the operating point only where the coupling is on. We achieve an average CZ gate fidelity of 98.3%, which is dominantly limited by qubit decoherence. The demonstrated tunable coupler provides a desirable tool to suppress adjacent qubit coupling and is suitable for large-scale quantum computation and simulation.
arxiv pdf

Perfect remote quantum state transfer in a superconducting qubit chain with parametrically tunable couplings

  1. X. Li,
  2. Y. Ma,
  3. J. Han,
  4. Tao Chen,
  5. Y. Xu,
  6. W. Cai,
  7. H. Wang,
  8. Y. P. Song,
  9. Zheng-Yuan Xue,
  10. Zhang-qi Yin,
  11. and Luyan Sun
Faithfully transferring quantum state is essential for quantum information processing. Here, we demonstrate a fast (in 84~ns) and high-fidelity (99.2%) quantum state transfer in a
chain of four superconducting qubits with nearest-neighbor coupling. This transfer relies on full control of the effective couplings between neighboring qubits, which is realized only by parametrically modulating the qubits without increasing circuit complexity. Once the couplings between qubits fulfill specific ratio, a perfect quantum state transfer can be achieved in a single step, therefore robust to noise and accumulation of experimental errors. This quantum state transfer can be extended to a larger qubit chain and thus adds a desirable tool for future quantum information processing. The demonstrated flexibility of the coupling tunability is suitable for quantum simulation of many-body physics which requires different configurations of qubit couplings.
arxiv pdf