R. P. G. McNeil

Magnetic-Field-Compatible Superconducting Transmon Qubit

  1. A. Kringhøj,
  2. T. W. Larsen,
  3. O. Erlandsson,
  4. W. Uilhoorn,
  5. J. G. Kroll,
  6. M. Hesselberg,
  7. R. P. G. McNeil,
  8. P. Krogstrup,
  9. L. Casparis,
  10. C. M. Marcus,
  11. and K. D. Petersson
We present a hybrid semiconductor-based superconducting qubit device which remains coherent at magnetic fields up to 1 T. The qubit transition frequency exhibits periodic oscillations
with magnetic field, consistent with interference effects due to the magnetic flux threading the cross section of the proximitized semiconductor nanowire junction. As induced superconductivity revives, additional coherent modes emerge at high magnetic fields, which we attribute to the interaction of the qubit and low-energy Andreev states.
arxiv pdf

A Parity-Protected Superconductor-Semiconductor Qubit

  1. T. W. Larsen,
  2. M.E. Gershenson,
  3. L. Casparis,
  4. A. Kringhøj,
  5. N. J. Pearson,
  6. R. P. G. McNeil,
  7. F. Kuemmeth,
  8. P. Krogstrup,
  9. K. D. Petersson,
  10. and C. M. Marcus
Coherence of superconducting qubits can be improved by implementing designs that protect the parity of Cooper pairs on superconducting islands. Here, we introduce a parity-protected
qubit based on voltage-controlled semiconductor nanowire Josephson junctions, taking advantage of the higher harmonic content in the energy-phase relation of few-channel junctions. A symmetric interferometer formed by two such junctions, gate-tuned into balance and frustrated by a half-quantum of applied flux, yields a cos(2{\phi}) Josephson element, reflecting coherent transport of pairs of Cooper pairs. We demonstrate that relaxation of the qubit can be suppressed ten-fold by tuning into the protected regime.
arxiv pdf