Masaaki Maezawa

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.
arxiv pdf

Toward Practical-Scale Quantum Annealing Machine for Prime Factoring

  1. Masaaki Maezawa,
  2. Go Fujii,
  3. Mutsuo Hidaka,
  4. Kentaro Imafuku,
  5. Katsuya Kikuchi,
  6. Hanpei Koike,
  7. Kazumasa Makise,
  8. Shuichi Nagasawa,
  9. Hiroshi Nakagawa,
  10. Masahiro Ukibe,
  11. and Shiro Kawabata
We propose a prime factorizer operated in a framework of quantum annealing (QA). The idea is inverse operation of a multiplier implemented with QA-based Boolean logic circuits. We designed
the QA machine on an application-specific-annealing-computing architecture which efficiently increases available hardware budgets at the cost of restricted functionality. The invertible operation of QA logic gates consisting of superconducting flux qubits was confirmed by circuit simulation with classical noise sources. The circuits were implemented and fabricated by using superconducting integrated circuit technologies with Nb/AlOx/Nb Josephson junctions. We also propose a 2.5Dimensional packaging scheme of a qubit-chip/interpose /package-substrate structure for realizing practically large-scale QA systems.
arxiv pdf