Trevyn F.Q. Larson

Localized quasiparticles in a fluxonium with quasi-two-dimensional amorphous kinetic inductors

  1. Trevyn F.Q. Larson,
  2. Sarah Garcia Jones,
  3. Tamás Kalmár,
  4. Pablo Aramburu Sanchez,
  5. Sai Pavan Chitta,
  6. Varun Verma,
  7. Kristen Genter,
  8. Katarina Cicak,
  9. Sae Woo Nam,
  10. Gergő Fülöp,
  11. Jens Koch,
  12. Ray W. Simmonds,
  13. and András Gyenis
Disordered superconducting materials with high kinetic inductance are an important resource to generate nonlinearity in quantum circuits and create high-impedance environments. In thin
films fabricated from these materials, the combination of disorder and the low effective dimensionality leads to increased order parameter fluctuations and enhanced kinetic inductance values. Among the challenges of harnessing these compounds in coherent devices are their proximity to the superconductor-insulator phase transition, the presence of broken Cooper pairs, and the two-level systems located in the disordered structure. In this work, we fabricate tungsten silicide wires from quasi-two-dimensional films with one spatial dimension smaller than the superconducting coherence length and embed them into microwave resonators and fluxonium qubits, where the kinetic inductance provides the inductive part of the circuits. We study the dependence of loss on the frequency, disorder, and geometry of the device, and find that the loss increases with the level of disorder and is dominated by the localized quasiparticles trapped in the spatial variations of the superconducting gap.
arxiv pdf

Fabrication and characterization of low-loss Al/Si/Al parallel plate capacitors for superconducting quantum information applications

  1. Anthony McFadden,
  2. Aranya Goswami,
  3. Tongyu Zhao,
  4. Teun van Schijndel,
  5. Trevyn F.Q. Larson,
  6. Sudhir Sahu,
  7. Stephen Gill,
  8. Florent Lecocq,
  9. Raymond Simmonds,
  10. and Chris Palmstrøm
Increasing the density of superconducting circuits requires compact components, however, superconductor-based capacitors typically perform worse as dimensions are reduced due to loss
at surfaces and interfaces. Here, parallel plate capacitors composed of aluminum-contacted, crystalline silicon fins are shown to be a promising technology for use in superconducting circuits by evaluating the performance of lumped element resonators and transmon qubits. High aspect ratio Si-fin capacitors having widths below 300nm with an approximate total height of 3μm are fabricated using anisotropic wet etching of Si(110) substrates followed by aluminum metallization. The single-crystal Si capacitors are incorporated in lumped element resonators and transmons by shunting them with lithographically patterned aluminum inductors and conventional Al/AlOx/Al Josephson junctions respectively. Microwave characterization of these devices suggests state-of-the-art performance for superconducting parallel plate capacitors with low power internal quality factor of lumped element resonators greater than 500k and qubit T1 times greater than 25μs. These results suggest that Si-Fins are a promising technology for applications that require low loss, compact, superconductor-based capacitors with minimal stray capacitance.
arxiv pdf