Charles Guinn

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

Microarchitectures for Heterogeneous Superconducting Quantum Computers

  1. Samuel Stein,
  2. Sara Sussman,
  3. Teague Tomesh,
  4. Charles Guinn,
  5. Esin Tureci,
  6. Sophia Fuhui Lin,
  7. Wei Tang,
  8. James Ang,
  9. Srivatsan Chakram,
  10. Ang Li,
  11. Margaret Martonosi,
  12. Fred T. Chong,
  13. Andrew A. Houck,
  14. Isaac L. Chuang,
  15. and Michael Austin DeMarco
Noisy Intermediate-Scale Quantum Computing (NISQ) has dominated headlines in recent years, with the longer-term vision of Fault-Tolerant Quantum Computation (FTQC) offering significant
potential albeit at currently intractable resource costs and quantum error correction (QEC) overheads. For problems of interest, FTQC will require millions of physical qubits with long coherence times, high-fidelity gates, and compact sizes to surpass classical systems. Just as heterogeneous specialization has offered scaling benefits in classical computing, it is likewise gaining interest in FTQC. However, systematic use of heterogeneity in either hardware or software elements of FTQC systems remains a serious challenge due to the vast design space and variable physical constraints. This paper meets the challenge of making heterogeneous FTQC design practical by introducing HetArch, a toolbox for designing heterogeneous quantum systems, and using it to explore heterogeneous design scenarios. Using a hierarchical approach, we successively break quantum algorithms into smaller operations (akin to classical application kernels), thus greatly simplifying the design space and resulting tradeoffs. Specializing to superconducting systems, we then design optimized heterogeneous hardware composed of varied superconducting devices, abstracting physical constraints into design rules that enable devices to be assembled into standard cells optimized for specific operations. Finally, we provide a heterogeneous design space exploration framework which reduces the simulation burden by a factor of 10^4 or more and allows us to characterize optimal design points. We use these techniques to design superconducting quantum modules for entanglement distillation, error correction, and code teleportation, reducing error rates by 2.6x, 10.7x, and 3.0x compared to homogeneous systems.
arxiv pdf