Michael Schleenvoigt

Thermal reconstruction as a method of substrate preparation for highly crystalline superconducting TiN resonators

  1. Thomas J. Smart,
  2. Marc Neis,
  3. Janine Lorenz,
  4. Marcello P. Guardascione,
  5. Roudy Hanna,
  6. Michael Schleenvoigt,
  7. Yuan Gao,
  8. Joscha Domnick,
  9. Benjamin Bennemann,
  10. Abdur Rehman Jalil,
  11. Jin Hee Bae,
  12. Harsh Bhardwaj,
  13. F. Stefan Tautz,
  14. Felix Lüpke,
  15. Detlev Grützmacher,
  16. Rami Barends,
  17. Pavel A. Bushev,
  18. and Peter Schüffelgen
High quality crystalline growth of a thin film on sapphire requires sufficient substrate preparation, often achieved via the use of aggressive chemical cleaning. Direct thermal reconstruction
of the sapphire substrate via a CO2 laser beam may allow for an alternative way to prepare the substrate for epitaxy without the use of any chemical processing. Within this work, we demonstrate that thermal annealing of sapphire into its (31‾‾‾√×31‾‾‾√)R±9° reconstruction is a valid alternative preparation technique for sapphire substrates. TiN films grown via plasma-assisted molecular beam epitaxy upon these substrates exhibit greater crystallinity than those grown on chemically cleaned sapphire substrates. Superconducting resonators fabricated from these films exhibit similar performance, with many possessing internal quality factors at single photon levels greater than 106 for both substrate preparation methods.
arxiv pdf

On-chip stencil lithography for superconducting qubits

  1. Roudy Hanna,
  2. Sören Ihssen,
  3. Simon Geisert,
  4. Umut Kocak,
  5. Matteo Arfini,
  6. Albert Hertel,
  7. Thomas J. Smart,
  8. Michael Schleenvoigt,
  9. Tobias Schmitt,
  10. Joscha Domnick,
  11. Kaycee Underwood,
  12. Abdur Rehman Jalil,
  13. Jin Hee Bae,
  14. Benjamin Bennemann,
  15. Mathieu Féchant,
  16. Mitchell Field,
  17. Martin Spiecker,
  18. Nicolas Zapata,
  19. Christian Dickel,
  20. Erwin Berenschot,
  21. Niels Tas,
  22. Gary A. Steele,
  23. Detlev Grützmacher,
  24. Ioan M. Pop,
  25. and Peter Schüffelgen
Improvements in circuit design and more recently in materials and surface cleaning have contributed to a rapid development of coherent superconducting qubits. However, organic resists
commonly used for shadow evaporation of Josephson junctions (JJs) pose limitations due to residual contamination, poor thermal stability and compatibility under typical surface-cleaning conditions. To provide an alternative, we developed an inorganic SiO2/Si3N4 on-chip stencil lithography mask for JJ fabrication. The stencil mask is resilient to aggressive cleaning agents and it withstands high temperatures up to 1200\textdegree{}C, thereby opening new avenues for JJ material exploration and interface optimization. To validate the concept, we performed shadow evaporation of Al-based transmon qubits followed by stencil mask lift-off using vapor hydrofluoric acid, which selectively etches SiO2. We demonstrate average $T_1 \approx 75 \pm 11~\SI{}{\micro\second}$ over a 200 MHz frequency range in multiple cool-downs for one device, and $T_1 \approx 44\pm 8~\SI{}{\micro\second}$ for a second device. These results confirm the compatibility of stencil lithography with state-of-the-art superconducting quantum devices and motivate further investigations into materials engineering, film deposition and surface cleaning techniques.
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