Kevin P. O'Brien

Broadband Microwave Isolation with Adiabatic Mode Conversion in Coupled Superconducting Transmission Lines

  1. Mahdi Naghiloo,
  2. Kaidong Peng,
  3. Yufeng Ye,
  4. Gregory Cunningham,
  5. and Kevin P. O'Brien
We propose a traveling wave scheme for broadband microwave isolation using parametric mode conversion in conjunction with adiabatic phase matching technique in a pair of coupled nonlinear
transmission lines. This scheme is compatible with the circuit quantum electrodynamics architecture (cQED) and provides isolation without introducing additional quantum noise. We first present the scheme in a general setting then propose an implementation with Josephson junction transmission lines. Numerical simulation shows more than 20 dB isolation over an octave bandwidth (4-8\,GHz) in a 2000 unit cell device with less than 0.05 dB insertion loss dominated by dielectric loss.
arxiv pdf

Randomized compiling for scalable quantum computing on a noisy superconducting quantum processor

  1. Akel Hashim,
  2. Ravi K. Naik,
  3. Alexis Morvan,
  4. Jean-Loup Ville,
  5. Bradley Mitchell,
  6. John Mark Kreikebaum,
  7. Marc Davis,
  8. Ethan Smith,
  9. Costin Iancu,
  10. Kevin P. O'Brien,
  11. Ian Hincks,
  12. Joel J. Wallman,
  13. Joseph Emerson,
  14. and Irfan Siddiqi
The successful implementation of algorithms on quantum processors relies on the accurate control of quantum bits (qubits) to perform logic gate operations. In this era of noisy intermediate-scale
quantum (NISQ) computing, systematic miscalibrations, drift, and crosstalk in the control of qubits can lead to a coherent form of error which has no classical analog. Coherent errors severely limit the performance of quantum algorithms in an unpredictable manner, and mitigating their impact is necessary for realizing reliable quantum computations. Moreover, the average error rates measured by randomized benchmarking and related protocols are not sensitive to the full impact of coherent errors, and therefore do not reliably predict the global performance of quantum algorithms, leaving us unprepared to validate the accuracy of future large-scale quantum computations. Randomized compiling is a protocol designed to overcome these performance limitations by converting coherent errors into stochastic noise, dramatically reducing unpredictable errors in quantum algorithms and enabling accurate predictions of algorithmic performance from error rates measured via cycle benchmarking. In this work, we demonstrate significant performance gains under randomized compiling for the four-qubit quantum Fourier transform algorithm and for random circuits of variable depth on a superconducting quantum processor. Additionally, we accurately predict algorithm performance using experimentally-measured error rates. Our results demonstrate that randomized compiling can be utilized to maximally-leverage and predict the capabilities of modern-day noisy quantum processors, paving the way forward for scalable quantum computing.
arxiv pdf