D. I. Santiago

Monitoring fast superconducting qubit dynamics using a neural network

  1. G. Koolstra,
  2. N. Stevenson,
  3. S. Barzili,
  4. L. Burns,
  5. K. Siva,
  6. S. Greenfield,
  7. W. Livingston,
  8. A. Hashim,
  9. R. K. Naik,
  10. J.M. Kreikebaum,
  11. K. P. O'Brien,
  12. D. I. Santiago,
  13. J. Dressel,
  14. and I. Siddiqi
Weak measurements of a superconducting qubit produce noisy voltage signals that are weakly correlated with the qubit state. To recover individual quantum trajectories from these noisy
signals, traditional methods require slow qubit dynamics and substantial prior information in the form of calibration experiments. Monitoring rapid qubit dynamics, e.g. during quantum gates, requires more complicated methods with increased demand for prior information. Here, we experimentally demonstrate an alternative method for accurately tracking rapidly driven superconducting qubit trajectories that uses a Long-Short Term Memory (LSTM) artificial neural network with minimal prior information. Despite few training assumptions, the LSTM produces trajectories that include qubit-readout resonator correlations due to a finite detection bandwidth. In addition to revealing rotated measurement eigenstates and a reduced measurement rate in agreement with theory for a fixed drive, the trained LSTM also correctly reconstructs evolution for an unknown drive with rapid modulation. Our work enables new applications of weak measurements with faster or initially unknown qubit dynamics, such as the diagnosis of coherent errors in quantum gates.
arxiv pdf

Qutrit randomized benchmarking

  1. A. Morvan,
  2. V. V. Ramasesh,
  3. M. S. Blok,
  4. J.M. Kreikebaum,
  5. K. O'Brien,
  6. L. Chen,
  7. B. K. Mitchell,
  8. R. K. Naik,
  9. D. I. Santiago,
  10. and I. Siddiqi
Ternary quantum processors offer significant computational advantages over conventional qubit technologies, leveraging the encoding and processing of quantum information in qutrits
(three-level systems). To evaluate and compare the performance of such emerging quantum hardware it is essential to have robust benchmarking methods suitable for a higher-dimensional Hilbert space. We demonstrate extensions of industry standard Randomized Benchmarking (RB) protocols, developed and used extensively for qubits, suitable for ternary quantum logic. Using a superconducting five-qutrit processor, we find a single-qutrit gate infidelity as low as 2.38×10−3. Through interleaved RB, we find that this qutrit gate error is largely limited by the native (qubit-like) gate fidelity, and employ simultaneous RB to fully characterize cross-talk errors. Finally, we apply cycle benchmarking to a two-qutrit CSUM gate and obtain a two-qutrit process fidelity of 0.82. Our results demonstrate a RB-based tool to characterize the obtain overall performance of a qutrit processor, and a general approach to diagnose control errors in future qudit hardware.
arxiv pdf