Jasmin Aghassi-Hagmann

Liquid metal printing for superconducting circuits

  1. Alexander Kreiner,
  2. Navid Hussain,
  3. Ritika Dhundhwal,
  4. Haoran Duan,
  5. Nicolas Zapata,
  6. Gabriel Cadilha Marques,
  7. Tino Cubaynes,
  8. Torsten Scherer,
  9. Wolfgang Wernsdorfer,
  10. Michael Hirtz,
  11. Ioan Mihai Pop,
  12. Jasmin Aghassi-Hagmann,
  13. and Thomas Reisinger
Superconducting circuits are a promising platform for implementing fault-tolerant quantum computers, quantum limited amplifiers, ultra-low power superconducting electronics, and sensors
with ultimate sensitivity. Typically, circuit fabrication is realized by standard nanolithography, generally associated with a high level of control over defects and contaminants. Additive approaches have not been used so far since they are expected to be inferior in terms of superconducting properties or quantum coherence. This work shows that liquid-metal based micro-pipette printing is suited for fabricating superconducting lumped-element resonators with high internal quality factors. The applicability of our technique for low-loss superconducting device fabrication and the possibility to locally add metal structures, without affecting any preexisting circuit elements, is a further advantage. Our results open up new avenues in the hardware implementation of scaled-up superconducting quantum computers.
arxiv pdf

High quality superconducting tantalum resonators with beta phase defects

  1. Ritika Dhundhwal,
  2. Haoran Duan,
  3. Lucas Brauch,
  4. Soroush Arabi,
  5. Dirk Fuchs,
  6. Amir-Abbas Haghighirad,
  7. Alexander Welle,
  8. Florentine Scharwaechter,
  9. Sudip Pal,
  10. Marc Scheffler,
  11. José Palomo,
  12. Zaki Leghtas,
  13. Anil Murani,
  14. Horst Hahn,
  15. Jasmin Aghassi-Hagmann,
  16. Christian Kübel,
  17. Wulf Wulfhekel,
  18. Ioan M. Pop,
  19. and Thomas Reisinger
For practical superconducting quantum processors, orders of magnitude improvement in coherence is required, motivating efforts to optimize hardware design and explore new materials.
Among the latter, the coherence of superconducting transmon qubits has been shown to improve by forming the qubit capacitor pads from α-tantalum, avoiding the meta-stable β-phase that forms when depositing tantalum at room temperature, and has been previously identified to be a source of microwave losses. In this work, we show lumped element resonators containing β-phase tantalum in the form of inclusions near the metal-substrate interface with internal quality factors (Qi) up to (5.0±2.5)×106 in the single photon regime. They outperform resonators with no sign of the β-phase in x-ray diffraction and thermal quasi-particle loss. Our results indicate that small concentrations of β-phase can be beneficial, enhancing critical magnetic fields and potentially, for improving coherence in tantalum based superconducting circuits.
arxiv pdf