Abstract
Superconducting quantum circuits underpin large-scale quantum processors and are increasingly interfaced with optical systems, yet they are vulnerable to quasiparticle poisoning from high-energy radiation and optical fields. Gap engineering of Josephson junctions suppresses quasiparticle-induced relaxation, but quasiparticles near the junction can still shift the qubit frequency and cause phase errors. Here, we extend gap engineering beyond the junction using a flux-tunable transmon with a gold-on-niobium ground plane and island and strongly gap-engineered aluminum junctions designed to keep quasiparticles away from the junction leads. Compared with an all-aluminum transmon with nominally identical junctions, we demonstrate that the niobium device withstands more than an order of magnitude higher near-infrared optical power before excess relaxation appears. The Nb transmon shows no resolvable quasiparticle-induced frequency shift over the same power range. At the same time, we observe that dephasing and state-preparation-and-measurement infidelity increase with optical power even while relaxation remains protected. These results suggest that engineering the quasiparticle energy landscape beyond the junction can substantially increase qubit resilience, not only to radiation-induced error bursts, but also to nearby optical fields.
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Cite this article
APA 7
Haug, T. H., Kolvik, J., Frey, J., Burger, P., Resare, F., Wieczorek, W., Gasparinetti, S., Delsing, P., & Van Laer, R. (2026). A quasiparticle-protected superconducting qubit. https://omanscience.com/en/articles/a-quasiparticle-protected-superconducting-qubit
MLA 9
Haug, Trond Hjerpekjøn, et al. "A quasiparticle-protected superconducting qubit." https://omanscience.com/en/articles/a-quasiparticle-protected-superconducting-qubit.
Chicago (author–date)
Haug, Trond Hjerpekjøn, Johan Kolvik, Joey Frey, Paul Burger, Fabian Resare, Witlef Wieczorek, Simone Gasparinetti, Per Delsing, and Raphaël Van Laer. 2026. "A quasiparticle-protected superconducting qubit." https://omanscience.com/en/articles/a-quasiparticle-protected-superconducting-qubit.
Harvard
Haug, T. H., Kolvik, J., Frey, J., Burger, P., Resare, F., Wieczorek, W., Gasparinetti, S., Delsing, P. and Van Laer, R. (2026) 'A quasiparticle-protected superconducting qubit', Available at: https://omanscience.com/en/articles/a-quasiparticle-protected-superconducting-qubit.
Vancouver
Haug TH, Kolvik J, Frey J, Burger P, Resare F, Wieczorek W, et al. A quasiparticle-protected superconducting qubit. https://omanscience.com/en/articles/a-quasiparticle-protected-superconducting-qubit
IEEE
T. H. Haug, J. Kolvik, J. Frey, P. Burger, F. Resare, W. Wieczorek, S. Gasparinetti, P. Delsing, and R. Van Laer, "A quasiparticle-protected superconducting qubit," https://omanscience.com/en/articles/a-quasiparticle-protected-superconducting-qubit.