B. L. T. Plourde

Process verification of two-qubit quantum gates by randomized benchmarking

  1. A. D. Córcoles,
  2. Jay M. Gambetta,
  3. Jerry M. Chow,
  4. John A. Smolin,
  5. Matthew Ware,
  6. J. D. Strand,
  7. B. L. T. Plourde,
  8. and M. Steffen
We implement a complete randomized benchmarking protocol on a system of two superconducting qubits. The protocol consists of randomizing over gates in the Clifford group, which experimentally
are generated via an improved two-qubit cross-resonance gate implementation and single-qubit unitaries. From this we extract an optimal average error per Clifford of 0.0936. We also perform an interleaved experiment, alternating our optimal two-qubit gate with random two-qubit Clifford gates, to obtain a two-qubit gate error of 0.0653. We compare these values with a two-qubit gate error of ~0.12 obtained from quantum process tomography, which is likely limited by state preparation and measurement errors.
arxiv pdf

Superconducting qubit in waveguide cavity with coherence time approaching 0.1ms

  1. Chad Rigetti,
  2. Stefano Poletto,
  3. Jay M. Gambetta,
  4. B. L. T. Plourde,
  5. Jerry M. Chow,
  6. A. D. Corcoles,
  7. John A. Smolin,
  8. Seth T. Merkel,
  9. J. R. Rozen,
  10. George A. Keefe,
  11. Mary B. Rothwell,
  12. Mark B. Ketchen,
  13. and M. Steffen
We report a superconducting artificial atom with an observed quantum coherence time of T2*=95us and energy relaxation time T1=70us. The system consists of a single Josephson junction
transmon qubit embedded in an otherwise empty copper waveguide cavity whose lowest eigenmode is dispersively coupled to the qubit transition. We attribute the factor of four increase in the coherence quality factor relative to previous reports to device modifications aimed at reducing qubit dephasing from residual cavity photons. This simple device holds great promise as a robust and easily produced artificial quantum system whose intrinsic coherence properties are sufficient to allow tests of quantum error correction.
arxiv pdf