W. J. Munro

Some implications of superconducting quantum interference to the application of master equations in engineering quantum technologies

  1. S.N.A. Duffus,
  2. K.N. Bjergstrøm,
  3. V.M. Dwyer,
  4. J.H. Samson,
  5. T.P. Spiller,
  6. W. J. Munro,
  7. Kae Nemoto,
  8. and M. J. Everitt
In this paper we consider the modelling and simulation of open quantum systems from a device engineering perspective. We derive master equations at different levels of approximation
for a Superconducting Quantum Interference Device (SQUID) ring coupled to an ohmic bath and demonstrate that the different levels of approximation produce qualitatively different dynamics. We discuss the issues raised when seeking to obtain Lindbladian dissipation and show, in this case, that the external flux (which may be considered to be a control variable in some applications) is not confined to the Hamiltonian, as often assumed in quantum control, but also appears in the Lindblad terms.
arxiv pdf

Analysis of the spectroscopy of a hybrid system composed of a superconducting flux qubit and diamond NV centers

  1. H. Cai,
  2. Y. Matsuzaki,
  3. K. Kakuyanagi,
  4. H. Toida,
  5. X. Zhu,
  6. N. Mizuochi,
  7. K. Nemoto,
  8. K. Semba,
  9. W. J. Munro,
  10. S. Saito,
  11. and H. Yamaguchi
A hybrid system that combines the advantages of a superconducting flux qubit and an electron spin ensemble in diamond is one of the promising devices to realize quantum information
processing. Exploring the properties of the superconductor diamond system is essential for the efficient use of this device. When we perform spectroscopy of this system, significant power broadening is observed. However, previous models to describe this system are known to be applicable only when the power broadening is negligible. Here, we construct a new approach to analyze this system with strong driving, and succeed to reproduce the spectrum with the power broadening. Our results provide an efficient way to analyze this hybrid system.
arxiv pdf

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