Takahiko Satoh

SU(4) gate design via unitary process tomography: its application to cross-resonance based superconducting quantum devices

  1. Michihiko Sugawara,
  2. and Takahiko Satoh
We present a novel approach for implementing pulse-efficient SU(4) gates on cross resonance (CR)-based superconducting quantum devices. Our method introduces a parameterized unitary
derived from the CR-Hamiltonian propagator, which accounts for static-ZZ interactions. Leveraging the Weyl chamber’s geometric structure, we successfully realize a continuous 2-qubit basis gate, RZZ(θ), as an echo-free pulse schedule on the IBM Quantum device ibm_kawasaki. We evaluate the average fidelity and gate time of various SU(4) gates generated using the RZZ(θ) to confirm the advantages of our implementation.
arxiv pdf

Ising interaction between capacitively-coupled superconducting flux qubits

  1. Takahiko Satoh,
  2. Yuichiro Matsuzaki,
  3. Kosuke Kakuyanagi,
  4. Koichi Semba,
  5. Hiroshi Yamaguchi,
  6. and Shiro Saito
Here, we propose a scheme to generate a controllable Ising interaction between superconducting flux qubits. Existing schemes rely on inducting couplings to realize Ising interactions
between flux qubits, and the interaction strength is controlled by an applied magnetic field On the other hand, we have found a way to generate an interaction between the flux qubits via capacitive couplings. This has an advantage in individual addressability, because we can control the interaction strength by changing an applied voltage that can be easily localized. This is a crucial step toward the realizing superconducting flux qubit quantum computation.
arxiv pdf