Lower-temperature fabrication of airbridges by grayscale lithography to increase yield of nanowire transmons in circuit QED quantum processors
T. Stavenga (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QCD/DiCarlo Lab)
M. S.A. Khan (University of Copenhagen, Danish Fundamental Metrology, Horsholm)
Y. Liu (University of Copenhagen)
P. Krogstrup (University of Copenhagen)
L. Dicarlo (TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/DiCarlo Lab, Kavli institute of nanoscience Delft, TU Delft - QN/DiCarlo Lab)
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Abstract
Quantum hardware based on circuit quantum electrodynamics makes extensive use of airbridges to suppress unwanted modes of wave propagation in coplanar-waveguide transmission lines. Airbridges also provide an interconnect enabling transmission lines to cross. Traditional airbridge fabrication produces a curved profile by reflowing resist at elevated temperature prior to metallization. The elevated temperature can affect the coupling energy and even yield of pre-fabricated Josephson elements of superconducting qubits, tunable couplers, and resonators. We employ grayscale lithography to enable reflow and thereby reduce the peak temperature of our airbridge fabrication process from 200 to 150 °C and link this change to a substantial increase in the physical yield of transmon qubits with Josephson elements realized using Al-contacted InAs nanowires.
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