Evolution of Nanowire Transmon Qubits and Their Coherence in a Magnetic Field
F. Luthi (TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/DiCarlo Lab, Kavli institute of nanoscience Delft)
Thijs Stavenga (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QCD/DiCarlo Lab)
O.W. Enzing (Student TU Delft, Kavli institute of nanoscience Delft)
A. Bruno (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QCD/DiCarlo Lab)
Christian Dickel (TU Delft - QCD/DiCarlo Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
NK Langford (TU Delft - QCD/DiCarlo Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
M. A. Rol (TU Delft - QCD/DiCarlo Lab, Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre)
T. S. Jespersen (University of Copenhagen)
Jesper Nygård (University of Copenhagen)
Peter Krogstrup (University of Copenhagen)
Leonardo di Carlo (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QN/DiCarlo Lab, TU Delft - QCD/DiCarlo Lab)
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Abstract
We present an experimental study of flux- and gate-tunable nanowire transmons with state-of-the-art relaxation time allowing quantitative extraction of flux and charge noise coupling to the Josephson energy. We evidence coherence sweet spots for charge, tuned by voltage on a proximal side gate, where first order sensitivity to switching two-level systems and background 1/f noise is minimized. Next, we investigate the evolution of a nanowire transmon in a parallel magnetic field up to 70 mT, the upper bound set by the closing of the induced gap. Several features observed in the field dependence of qubit energy relaxation and dephasing times are not fully understood. Using nanowires with a thinner, partially covering Al shell will enable operation of these circuits up to 0.5 T, a regime relevant for topological quantum computation and other applications.