Quasiparticle Dynamics in Superconducting Quantum-Classical Hybrid Circuits

  1. Kuang Liu,
  2. Xiaoliang He,
  3. Zhengqi Niu,
  4. Hang Xue,
  5. Wenbing Jiang,
  6. Liliang Ying,
  7. Wei Peng,
  8. Masaaki Maezawa,
  9. Zhirong Lin,
  10. Xiaoming Xie,
  11. and Zhen Wang
Single flux quantum (SFQ) circuitry is a promising candidate for a scalable and integratable cryogenic quantum control system. However, the operation of SFQ circuits introduces non-equilibrium quasiparticles (QPs), which are a significant source of qubit decoherence. In this study, we investigate QP behavior in a superconducting quantum-classical hybrid chip that comprises an SFQ circuit and a qubit circuit. By monitoring qubit relaxation time, we explore the dynamics of SFQ-circuit-induced QPs. Our findings reveal that the QP density near the qubit reaches its peak after several microseconds of SFQ circuit operation, which corresponds to the phonon-mediated propagation time of QPs in the hybrid circuits. This suggests that phonon-mediated propagation dominates the spreading of QPs in the hybrid circuits. Our results lay the foundation to suppress QP poisoning in quantum-classical hybrid systems.
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