Junction-Intrinsic Dissipation in Hybrid Superconductor-Semiconductor Gatemon Qubits

Quantum Physics [Submitted on 31 Mar 2026] Junction-Intrinsic Dissipation in Hybrid Superconductor-Semiconductor Gatemon Qubits Zhenhai Sun, David Feldstein-Bofill, Ksenia Shagalov, Amalie T. J. Paulsen, Casper Wied, Shikhar Singh, Brian D. Isakov, Jacob Hastrup, Christopher W. Warren, Svend Krøjer, Anders Kringhøj, András Gyenis, Morten Kjaergaard Superconducting transmon qubits based on hybrid superconductor-semiconductor Josephson junctions (gatemons) offer gate tunability, but their relaxation times remain well below those of state-of-the-art transmons, and the origin of this discrepancy is not fully understood. Here, we co-fabricate gatemons and SIS-junction transmons with nominally identical circuit layouts, gate dielectrics, and control lines, so that the Josephson element is the only intentional distinction. Across multiple chips, transmons in this architecture reach relaxation times in the tens of microseconds, whereas gatemons saturate in the few-microsecond range. Using the transmons as on-chip references, we construct a loss budget including Purcell decay, spontaneous emission through the control line, and internal dielectric loss, and find that the corresponding T1 limits exceed all measured gatemon values by more than an order of magnitude. Temperature-dependent T1 measurements follow a common quasiparticle-activation model and yield similar superconducting gaps for S-Sm-S and SIS junctions, indicating that the reduced gatemon coherence is dominated by additional temperature-independent, junction-intrinsic dissipation. Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall) Cite as: arXiv:2603.29498 [quant-ph]   (or arXiv:2603.29498v1 [quant-ph] for this version)   https://doi.org/10.48550/arXiv.2603.29498 Focus to learn more Submission history From: Zhenhai Sun [view email] [v1] Tue, 31 Mar 2026 09:41:08 UTC (8,942 KB) Access Paper: HTML (experimental) view license Current browse context: quant-ph < prev   |   next > new | recent | 2026-03 Change to browse by: cond-mat cond-mat.mes-hall References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)