P. A. Spring

Selective Excitation of Superconducting Qubits with a Shared Control Line through Pulse Shaping

  1. R. Matsuda,
  2. R. Ohira,
  3. T. Sumida,
  4. H. Shiomi,
  5. A. Machino,
  6. S. Morisaka,
  7. K. Koike,
  8. T. Miyoshi,
  9. Y. Kurimoto,
  10. Y. Sugita,
  11. Y. Ito,
  12. Y. Suzuki,
  13. P. A. Spring,
  14. S. Wang,
  15. S. Tamate,
  16. Y. Tabuchi,
  17. Y. Nakamura,
  18. K. Ogawa,
  19. and M. Negoro
In conventional architectures of superconducting quantum computers, each qubit is connected to its own control line, leading to a commensurate increase in the number of microwave lines
as the system scales. Frequency-multiplexed qubit-control addresses this problem by enabling multiple qubits to share a single microwave line. However, it can cause unwanted excitation of non-target qubits, especially when the detuning between qubits is smaller than the pulse bandwidth. Here, we propose a selective-excitation-pulse (SEP) technique that suppresses unwanted excitations by shaping a drive pulse to create null points at non-target qubit frequencies. In a proof-of-concept experiment with three fixed-frequency transmon qubits, we demonstrate that the SEP technique achieves single-qubit gate fidelities comparable to those obtained with conventional Gaussian pulses while effectively suppressing unwanted excitations in non-target qubits. These results highlight the SEP technique as a promising tool for enhancing frequency-multiplexed qubit-control.
arxiv pdf

Modelling of TM Modes in Periodically-Shorted Cavities for Circuit QED

  1. P. A. Spring,
  2. S. Sosnina,
  3. T. Tsunoda,
  4. B. Vlastakis,
  5. and P. J. Leek
Electromagnetic cavities are ubiquitous in superconducting quantum circuit research, employed to control a circuit’s electromagnetic environment, suppress radiative loss, and
implement functionalities such as qubit readout and inter-qubit coupling. Here we consider the case of a rectangular cavity shorted by a periodic array of conducting cylinders. This is a potential enclosure geometry for large-scale quantum chips with many qubits. We develop simple, accurate models for the TM modes of the cavity, over a wide range of cylinder spacing and radii, using a plasma model and a coupled cavity array circuit model. We compare predictions with finite-element simulation and find good agreement. We investigate inter-qubit couplings mediated by such cavities for circuits at the 100-qubit scale, and discuss additional applications to circuit QED.
arxiv pdf