Symmetrically Threaded Superconducting Quantum Interference Devices as Next-Generation Kerr-Cat Qubits

Authors

Bibek Bhandari, Chapman University
Irwin Huang, University of Rochester
Ahmed Hajr, University of California - Berkeley
Kagan Yanik, University of Rochester
Bingcheng Qing, University of California - Berkeley
Ke Wang, University of California - Berkeley
David I. Santiago, University of California - Berkeley
Justin Dressel, Chapman UniversityFollow
Irfan Siddiqi, University of California - Berkeley
Andrew N. Jordan, Chapman UniversityFollow

Document Type

Article

Publication Date

8-29-2025

Abstract

Kerr-cat qubits are bosonic qubits offering autonomous bit-flip protection, traditionally studied using driven superconducting nonlinear asymmetric inductive element (SNAIL) oscillators. Here, we theoretically explore an alternative circuit for Kerr-cat qubits based on symmetrically threaded superconducting quantum interference devices (SQUIDs). The symmetrically threaded SQUID (STS) architecture employs a simplified flux-pumped design that suppresses two-photon dissipation, a dominant loss mechanism in high-Kerr regimes, by engineering the drive Hamiltonian’s flux operator to generate only even-order harmonics. By fulfilling two critical criteria for practical Kerr-cat qubit operation, the STS emerges as an ideal platform: (1) a static Hamiltonian with diluted Kerr nonlinearity (achieved via the STS’s middle branch) and (2) a drive Hamiltonian restricted to even harmonics, which ensures robust two-photon driving with reduced dissipation. For weak Kerr nonlinearity, we find that the coherent state lifetime (T_α) is similar between STS and SNAIL circuits. However, STS Kerr-cat qubits exhibit enhanced resistance to higher-order photon dissipation, enabling significantly extended T_α even with stronger Kerr nonlinearities (approximately 10 MHz). In contrast to SNAIL, STS Kerr-cat qubits display a T_α dip under weak twophoton driving for a high Kerr coefficient. We demonstrate that this dip can be suppressed by applying drive-dependent detuning, enabling Kerr-cat qubit operation with only eight Josephson junctions (of energies 80 GHz); fewer junctions suffice for higher junction energies. We further validate the robustness of the STS design by studying the impact of strong flux driving and asymmetric Josephson junctions on T_α. With the proposed design and considering a cat size of ten photons, we predict T_α of the order of tens of milliseconds, even in the presence of multiphoton heating and dephasing effects. The robustness of the STS Kerr-cat qubit makes it a promising component for fault-tolerant quantum processors.

Comments

This article was originally published in PRX Quantum, volume 6, in 2025. https://doi.org/10.1103/c661-yr2z

Recommended Citation

B. Bhandari, I. Huang, A. Hajr, K. Yanik, B. Qing, K. Wang, D. I. Santiago, J. Dressel, I. Siddiqi, and A. N. Jordan, Symmetrically threaded superconducting quantum interference devices as next-generation Kerr-Cat qubits, PRX Quantum 6, 030338 (2025). https://doi.org/10.1103/c661-yr2z

Peer Reviewed

1

Copyright

The authors

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This work is licensed under a Creative Commons Attribution 4.0 License.