N. J. Pearson

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

Voltage-Controlled Superconducting Quantum Bus

  1. L. Casparis,
  2. N. J. Pearson,
  3. A. Kringhøj,
  4. T. W. Larsen,
  5. F. Kuemmeth,
  6. J. Nygård,
  7. P. Krogstrup,
  8. K. D. Petersson,
  9. and C. M. Marcus
We demonstrate the ability of an epitaxial semiconductor-superconductor nanowire to serve as a field-effect switch to tune a superconducting cavity. Two superconducting gatemon qubits
are coupled to the cavity, which acts as a quantum bus. Using a gate voltage to control the superconducting switch yields up to a factor of 8 change in qubit-qubit coupling between the on and off states without detrimental effect on qubit coherence. High-bandwidth operation of the coupling switch on nanosecond timescales degrades qubit coherence.
arxiv pdf