B. Chiaro

Multiplexed dispersive readout of superconducting phase qubits

  1. Yu Chen,
  2. D. Sank,
  3. P. O'Malley,
  4. T. White,
  5. R. Barends,
  6. B. Chiaro,
  7. J. Kelly,
  8. E. Lucero,
  9. M. Mariantoni,
  10. A. Megrant,
  11. C. Neill,
  12. A. Vainsencher,
  13. J. Wenner,
  14. Yi Yin,
  15. A. N. Cleland,
  16. and John M. Martinis
We introduce a frequency-multiplexed readout scheme for superconducting phase qubits. Using a quantum circuit with four phase qubits, we couple each qubit to a separate lumped-element
superconducting readout resonator, with the readout resonators connected in parallel to a single measurement line. The readout resonators and control electronics are designed so that all four qubits can be read out simultaneously using frequency multiplexing on the one measurement line. This technology provides a highly efficient and compact means for reading out multiple qubits, a significant advantage for scaling up to larger numbers of qubits.
arxiv pdf

Excitation of superconducting qubits from hot non-equilibrium quasiparticles

  1. J. Wenner,
  2. Yi Yin,
  3. Erik Lucero,
  4. R. Barends,
  5. Yu Chen,
  6. B. Chiaro,
  7. J. Kelly,
  8. M. Lenander,
  9. Matteo Mariantoni,
  10. A. Megrant,
  11. C. Neill,
  12. P. J. J. O'Malley,
  13. D. Sank,
  14. A. Vainsencher,
  15. H. Wang,
  16. T. C. White,
  17. A. N. Cleland,
  18. and John M. Martinis
Superconducting qubits probe environmental defects such as non-equilibrium quasiparticles, an important source of decoherence. We show that „hot“ non-equilibrium quasiparticles,
with energies above the superconducting gap, affect qubits differently from quasiparticles at the gap, implying qubits can probe the dynamic quasiparticle energy distribution. For hot quasiparticles, we predict a non-neligable increase in the qubit excited state probability P_e. By injecting hot quasiparticles into a qubit, we experimentally measure an increase of P_e in semi-quantitative agreement with the model.
arxiv pdf