Norikazu Mizuochi

Improving the lifetime of the NV center ensemble coupled with a superconducting flux qubit by applying magnetic fields

  1. Yuichiro Matsuzaki,
  2. Xiaobo Zhu,
  3. Kosuke Kakuyanagi,
  4. Hiraku Toida,
  5. Takaaki Shimooka,
  6. Norikazu Mizuochi,
  7. Kae Nemoto,
  8. Kouichi Semba,
  9. W. J. Munro,
  10. Hiroshi Yamaguchi,
  11. and Shiro Saito
One of the promising systems to realize quantum computation is a hybrid system where a superconducting flux qubit plays a role of a quantum processor and the NV center ensemble is used
as a quantum memory. We have theoretically and experimentally studied the effect of magnetic fields on this hybrid system, and found that the lifetime of the vacuum Rabi oscillation is improved by applying a few mT magnetic field to the NV center ensemble. Here, we construct a theoretical model to reproduce the vacuum Rabi oscillations with/without magnetic fields applied to the NV centers, and we determine the reason why magnetic fields can affect the coherent properties of the NV center ensemble. From our theoretical analysis, we quantitatively show that the magnetic fields actually suppress the inhomogeneous broadening from the strain in the NV centers.
arxiv pdf

Towards Realizing a Quantum Memory for a Superconducting Qubit: Storage and Retrieval of quantum states

  1. Shiro Saito,
  2. Xiaobo Zhu,
  3. Robert Amsüss,
  4. Yuichiro Matsuzaki,
  5. Kosuke Kakuyanagi,
  6. Takaaki Shimo-Oka,
  7. Norikazu Mizuochi,
  8. Kae Nemoto,
  9. William J. Munro,
  10. and Kouichi Semba
We have built a hybrid system composed of a superconducting flux qubit (the processor) and an ensemble of nitrogen-vacancy centers in diamond (the memory) that can be directly coupled
to one another and demonstrated how information can be transferred from the flux qubit to the memory, stored and subsequently retrieved. We have established the coherence properties of the memory, and succeeded in creating an entangled state between the processor and memory, demonstrating how the entangled state’s coherence is preserved. Our results are a significant step towards using an electron spin ensemble as a quantum memory for superconducting qubits.
arxiv pdf