Entangling remote microwave quantum computers with hybrid entanglement swap and variational distillation

  1. Bingzhi Zhang,
  2. Jing Wu,
  3. Linran Fan,
  4. and Quntao Zhuang
Superconducting microwave circuits with Josephson junctions are a major platform for quantum computing. To unleash their full capabilities, the cooperative operation of multiple microwave
superconducting circuits is required. Therefore, designing an efficient protocol to distribute microwave entanglement remotely becomes a crucial open problem. Here, we propose a continuous-variable entanglement-swap approach based on optical-microwave entanglement generation, which can boost the ultimate rate by two orders of magnitude at state-of-the-art parameter region, compared with traditional approaches. We further empower the protocol with a hybrid variational entanglement distillation component to provide huge advantage in the infidelity-versus-success-probability trade-off. Our protocol can be realized with near-term device performance, and is robust against non-perfections such as optical loss and noise. Therefore, our work provides a practical method to realize efficient quantum links for superconducting microwave quantum computers.

Superconducting cavity electro-optics: a platform for coherent photon conversion between superconducting and photonic circuits

  1. Linran Fan,
  2. Chang-Ling Zou,
  3. Risheng Cheng,
  4. Xiang Guo,
  5. Xu Han,
  6. Zheng Gong,
  7. Sihao Wang,
  8. and Hong X. Tang
Leveraging the quantum information processing ability of superconducting circuits and long-distance distribution ability of optical photons promises the realization of complex and large-scale
quantum networks. In such a scheme, a coherent and efficient quantum transducer between superconducting and photonic circuits is critical. However, such quantum transducer is still challenging since the use of intermediate excitations in current schemes introduces extra noise and limits bandwidth. Here we realize direct and coherent transduction between superconducting and photonic circuits based on triple-resonance electro-optics principle, with integrated devices incorporating both superconducting and optical cavities on the same chip. Electromagnetically induced transparency is observed, indicating the coherent interaction between microwave and optical photons. Internal conversion efficiency of 25.9\pm0.3\% has been achieved, with 2.05\pm0.04\% total efficiency. Superconducting cavity electro-optics offers broad transduction bandwidth and high scalability, and represents a significant step towards the integrated hybrid quantum circuits and distributed quantum computation.