Sai Pavan Chitta

Tunable inductive coupler for high fidelity gates between fluxonium qubits

  1. Helin Zhang,
  2. Chunyang Ding,
  3. D. K. Weiss,
  4. Ziwen Huang,
  5. Yuwei Ma,
  6. Charles Guinn,
  7. Sara Sussman,
  8. Sai Pavan Chitta,
  9. Danyang Chen,
  10. Andrew A. Houck,
  11. Jens Koch,
  12. and David I. Schuster
The fluxonium qubit is a promising candidate for quantum computation due to its long coherence times and large anharmonicity. We present a tunable coupler that realizes strong inductivecoupling between two heavy-fluxonium qubits, each with ∼50MHz frequencies and ∼5 GHz anharmonicities. The coupler enables the qubits to have a large tuning range of XX coupling strengths (−35 to 75 MHz). The ZZ coupling strength is <3kHz across the entire coupler bias range, and <100Hz at the coupler off-position. These qualities lead to fast, high-fidelity single- and two-qubit gates. By driving at the difference frequency of the two qubits, we realize a iSWAP‾‾‾‾‾‾‾√ gate in 258ns with fidelity 99.72%, and by driving at the sum frequency of the two qubits, we achieve a bSWAP‾‾‾‾‾‾‾‾√ gate in 102ns with fidelity 99.91%. This latter gate is only 5 qubit Larmor periods in length. We run cross-entropy benchmarking for over 20 consecutive hours and measure stable gate fidelities, with bSWAP‾‾‾‾‾‾‾‾√ drift (2σ) <0.02% and iSWAP‾‾‾‾‾‾‾√ drift <0.08%.[/expand]
arxiv pdf

Computer-aided quantization and numerical analysis of superconducting circuits

  1. Sai Pavan Chitta,
  2. Tianpu Zhao,
  3. Ziwen Huang,
  4. Ian Mondragon-Shem,
  5. and Jens Koch
The development of new superconducting circuits and the improvement of existing ones rely on the accurate modeling of spectral properties which are key to achieving the needed advances
in qubit performance. Systematic circuit analysis at the lumped-element level, starting from a circuit network and culminating in a Hamiltonian appropriately describing the quantum properties of the circuit, is a well-established procedure, yet cumbersome to carry out manually for larger circuits. We present work utilizing symbolic computer algebra and numerical diagonalization routines versatile enough to tackle a variety of circuits. Results from this work are accessible through a newly released module of the scqubits package.
arxiv pdf