Karl D. Petersson

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

Destructive Little-Parks Effect in a Full-Shell Nanowire-based Transmon

  1. Deividas Sabonis,
  2. Oscar Erlandsson,
  3. Anders Kringhøj,
  4. Bernard van Heck,
  5. Thorvald W. Larsen,
  6. Ivana Petkovic,
  7. Peter Krogstrup,
  8. Karl D. Petersson,
  9. and Charles M. Marcus
A semiconductor transmon with an epitaxial Al shell fully surrounding an InAs nanowire core is investigated in the low EJ/EC regime. Little-Parks oscillations as a function of fluxalong the hybrid wire axis are destructive, creating lobes of reentrant superconductivity separated by a metallic state at a half-quantum of applied flux. In the first lobe, phase winding around the shell can induce topological superconductivity in the core. Coherent qubit operation is observed in both the zeroth and first lobes. Splitting of parity bands by coherent single-electron coupling across the junction is not resolved beyond line broadening, placing a bound on Majorana coupling, EM/h < 10 MHz, much smaller than the Josephson coupling EJ/h ~ 4.7 GHz.[/expand]
arxiv pdf

Superconducting Gatemon Qubit based on a Proximitized Two-Dimensional Electron Gas

  1. Lucas Casparis,
  2. Malcolm R. Connolly,
  3. Morten Kjaergaard,
  4. Natalie J. Pearson,
  5. Anders Kringhøj,
  6. Thorvald W. Larsen,
  7. Ferdinand Kuemmeth,
  8. Tiantian Wang,
  9. Candice Thomas,
  10. Sergei Gronin,
  11. Geoffrey C. Gardner,
  12. Michael J. Manfra,
  13. Charles M. Marcus,
  14. and Karl D. Petersson
The coherent tunnelling of Cooper pairs across Josephson junctions (JJs) generates a nonlinear inductance that is used extensively in quantum information processors based on superconducting
circuits, from setting qubit transition frequencies and interqubit coupling strengths, to the gain of parametric amplifiers for quantum-limited readout. The inductance is either set by tailoring the metal-oxide dimensions of single JJs, or magnetically tuned by parallelizing multiple JJs in superconducting quantum interference devices (SQUIDs) with local current-biased flux lines. JJs based on superconductor-semiconductor hybrids represent a tantalizing all-electric alternative. The gatemon is a recently developed transmon variant which employs locally gated nanowire (NW) superconductor-semiconductor JJs for qubit control. Here, we go beyond proof-of-concept and demonstrate that semiconducting channels etched from a wafer-scale two-dimensional electron gas (2DEG) are a suitable platform for building a scalable gatemon-based quantum computer. We show 2DEG gatemons meet the requirements by performing voltage-controlled single qubit rotations and two-qubit swap operations. We measure qubit coherence times up to ~2 us, limited by dielectric loss in the 2DEG host substrate.
arxiv pdf