Qubit ZooControlled comparison of co-fabricated gatemons and tunnel-junction transmons with nominally identical layouts, isolating an additional loss channel associated with the hybrid semiconductor junction.
Abstract
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.
Key Findings
- A representative matched pair yielded gatemon at 3.70 GHz and transmon at 4.21 GHz.
- Purcell decay, control-line spontaneous emission, and inferred dielectric loss predicted lifetimes more than an order of magnitude above the measured gatemon values.
- Temperature-dependent measurements were consistent with an additional temperature-independent, junction-intrinsic dissipation channel.
Links
- arXiv: 2603.29498
Verification Report
Verification status: verified. Disputes resolved: 0. Citation count snapshot (Semantic Scholar): 0. Ingestion source: latex. Text truncated: no.