Tobias Lindström

Long-lived memory effects in the defect bath of superconducting qubits

  1. Abhishek Agarwal,
  2. Masum Uddin,
  3. Shroya Vaidya,
  4. Lachlan P. Lindoy,
  5. Ehsaneh Daghigh Ahmadi,
  6. Tobias Lindström,
  7. Sebastian E. de Graaf,
  8. and Ivan Rungger
We reveal long-lived memory effects in the defect bath of a superconducting transmon qubit through electric-field tuning of two-level system (TLS) defects coupled to the qubit. Using
a fast TLS mapping method we observe several hysteretic effects in the TLS environment with memory timescales of the order of seconds, far beyond the lifetimes of individual TLS defects. The observations can be explained by TLS coupling to electric field-polarised charge fluctuators in the defect bath. Our method enables detailed mapping of the dynamics of the bath’s coupled microscopic degrees of freedom and the associated memory effects which can introduce temporally correlated noise. This information may be used to improve qubit-stabilisation and quantum error correction protocols.
arxiv pdf

Integration of selectively grown topological insulator nanoribbons in superconducting quantum circuits

  1. Tobias W. Schmitt,
  2. Malcolm R. Connolly,
  3. Michael Schleenvoigt,
  4. Chenlu Liu,
  5. Oscar Kennedy,
  6. Abdur R. Jalil,
  7. Benjamin Bennemann,
  8. Stefan Trellenkamp,
  9. Florian Lentz,
  10. Elmar Neumann,
  11. Tobias Lindström,
  12. Sebastian E. de Graaf,
  13. Erwin Berenschot,
  14. Niels Tas,
  15. Gregor Mussler,
  16. Karl D. Petersson,
  17. Detlev Grützmacher,
  18. and Peter Schüffelgen
We report on the precise integration of nm-scale topological insulator Josephson junctions into mm-scale superconducting quantum circuits via selective area epitaxy and local stencil
lithography. By studying dielectric losses of superconducting microwave resonators fabricated on top of our selective area growth mask, we verify the compatibility of this in situ technique with microwave applications. We probe the microwave response of on-chip microwave cavities coupled to topological insulator-shunted superconducting qubit devices and observe a power dependence that indicates nonlinear qubit behaviour. Our method enables integration of complex networks of topological insulator nanostructures into superconducting circuits, paving the way for both novel voltage-controlled Josephson and topological qubits.
arxiv pdf