G. B. P. Huber

Robust multi-mode superconducting qubit designed with evolutionary algorithms

  1. P. García-Azorín,
  2. F. A. Cárdenas-López,
  3. G. B. P. Huber,
  4. G. Romero,
  5. M. Werninghaus,
  6. F. Motzoi,
  7. S. Filipp,
  8. and M. Sanz
Multi-mode superconducting circuits offer a promising platform for engineering robust systems for quantum computation. Previous studies have shown that single-mode devices cannot simultaneously
exhibit resilience against multiple decoherence sources due to conflicting protection requirements. In contrast, multi-mode systems offer increased flexibility and have proven capable of overcoming these fundamental limitations. Nevertheless, exploring multi-mode architectures is computationally demanding due to the exponential scaling of the Hilbert space dimension. Here, we present a multi-mode device designed using evolutionary optimization techniques, which have been shown to be effective for this computational task. The proposed device was optimized to feature an anharmonicity of a third of the qubit frequency and reduced energy dispersion caused by charge and magnetic flux fluctuations. It exhibits improvements over the fundamental errors limiting Transmon and Fluxonium coherence and manipulation, aiming for a balance between low depolarization error and fast manipulation; furthermore demonstrating robustness against fabrication errors, a major limitation in many proposed multi-mode devices. Overall, by striking a balance between coupling matrix elements and noise protection, we propose a device that paves the way towards finding proper characteristics for the construction of superconducting quantum processors.
arxiv pdf

Parametric multi-element coupling architecture for coherent and dissipative control of superconducting qubits

  1. G. B. P. Huber,
  2. F. A. Roy,
  3. L. Koch,
  4. I. Tsitsilin,
  5. J. Schirk,
  6. N. J. Glaser,
  7. N. Bruckmoser,
  8. C. Schweizer,
  9. J. Romeiro,
  10. G. Krylov,
  11. M. Singh,
  12. F. X. Haslbeck,
  13. M. Knudsen,
  14. A. Marx,
  15. F. Pfeiffer,
  16. C. Schneider,
  17. F. Wallner,
  18. D. Bunch,
  19. L. Richard,
  20. L. Södergren,
  21. K. Liegener,
  22. M. Werninghaus,
  23. and S. Filipp
As systems for quantum computing keep growing in size and number of qubits, challenges in scaling the control capabilities are becoming increasingly relevant. Efficient schemes to simultaneously
mediate coherent interactions between multiple quantum systems and to reduce decoherence errors can minimize the control overhead in next-generation quantum processors. Here, we present a superconducting qubit architecture based on tunable parametric interactions to perform two-qubit gates, reset, leakage recovery and to read out the qubits. In this architecture, parametrically driven multi-element couplers selectively couple qubits to resonators and neighbouring qubits, according to the frequency of the drive. We consider a system with two qubits and one readout resonator interacting via a single coupling circuit and experimentally demonstrate a controlled-Z gate with a fidelity of 98.30±0.23%, a reset operation that unconditionally prepares the qubit ground state with a fidelity of 99.80±0.02% and a leakage recovery operation with a 98.5±0.3% success probability. Furthermore, we implement a parametric readout with a single-shot assignment fidelity of 88.0±0.4%. These operations are all realized using a single tunable coupler, demonstrating the experimental feasibility of the proposed architecture and its potential for reducing the system complexity in scalable quantum processors.
arxiv pdf