Ayuka Morioka

Change in bit-flip times of Kerr parametric oscillators caused by their interactions

  1. Yuya Kano,
  2. Yohei Kawakami,
  3. Shumpei Masuda,
  4. Tomohiro Yamaji,
  5. Aiko Yamaguchi,
  6. Tetsuro Satoh,
  7. Ayuka Morioka,
  8. Kiyotaka Endo,
  9. Yuichi Igarashi,
  10. Masayuki Shirane,
  11. and Tsuyoshi Yamamoto
We experimentally investigate how interactions between Kerr parametric oscillators (KPOs) degrade their bit-flip times, where a bit flip is defined as a transition between the two degenerate
ground states of a KPO. Interactions between KPOs cause quantum states of KPOs to leak outside the computational subspace, leading to bit flips. Bit flips degrade fidelity and pose a significant problem for KPO-based quantum information processing. We performed an experiment in which a weak microwave signal is injected into one KPO to emulate photon injection from another KPO, and find that the bit-flip time decreases by an order of magnitude due to induced excitations, depending on the frequency and power of the injected signal. Methods to mitigate the decrease in bit-flip times caused by interactions between KPOs are discussed, including adjusting the pump frequencies, coherent-state amplitudes, and couplings between KPOs. These findings provide valuable insights for scaling up KPO-based quantum computers.
arxiv pdf

Four-body interactions in Kerr parametric oscillator circuits

  1. Yohei Kawakami,
  2. Tomohiro Yamaji,
  3. Aiko Yamaguchi,
  4. Yuya Kano,
  5. Takaaki Aoki,
  6. Aree Taguchi,
  7. Kiyotaka Endo,
  8. Tetsuro Satoh,
  9. Ayuka Morioka,
  10. Yuichi Igarashi,
  11. Masayuki Shirane,
  12. and Tsuyoshi Yamamoto
We theoretically present new unit circuits of Kerr parametric oscillators (KPOs) with four-body interactions, which enable the scalable embedding of all-to-all connected logical Ising
spins using the Lechner-Hauke-Zoller (LHZ) scheme. These unit circuits enable four-body interactions using linear couplers, making the circuit fabrication and characterization much simpler than those of conventional unit circuits with nonlinear couplers. Numerical calculations indicate that the magnitudes of the coupling constants can be comparable to those in conventional circuits. On the basis of this theory, we designed a four-KPO circuit and experimentally confirmed the four-body correlation by measuring the pump-phase dependence of the parity of the four-KPO states. We show that the choice of the pump frequencies are important not only to enable the four-body interaction, but to cancel the effects of other unwanted interactions. Using the circuit, we demonstrated the quantum annealing based on the LHZ scheme, where the strength of the interaction between the logical Ising spins is mapped to the local field and controlled by a coherent drive applied to each KPO.
arxiv pdf