L. Chen

Multipartite Entanglement in Rabi Driven Superconducting Qubits

  1. M. Lu,
  2. J. L. Ville,
  3. J. Cohen,
  4. A. Petrescu,
  5. S. Schreppler,
  6. L. Chen,
  7. C. Jüenger,
  8. C. Pelletti,
  9. A. Marchenkov,
  10. A. Banerjee,
  11. W. Livingston,
  12. J.M. Kreikebaum,
  13. D. Santiago,
  14. A. Blais,
  15. and I. Siddiqi
Exploring highly connected networks of qubits is invaluable for implementing various quantum algorithms and simulations as it allows for entangling qubits with reduced circuit depth.
Here, we demonstrate a multi-qubit STAR (Sideband Tone Assisted Rabi driven) gate. Our scheme is inspired by the ion qubit Mølmer-Sørensen gate and is mediated by a shared photonic mode and Rabi-driven superconducting qubits, which relaxes restrictions on qubit frequencies during fabrication and supports scalability. We achieve a two-qubit gate with maximum state fidelity of 0.95 in 310 ns, a three-qubit gate with state fidelity 0.905\% in 217 ns, and a four-qubit gate with state fidelity 0.66 in 200 ns. Furthermore, we develop a model of the gate that show the four-qubit gate is limited by shared resonator losses and the spread of qubit-resonator couplings, which must be addressed to reach high-fidelity operations.
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