Millisecond lifetimes and coherence times in 2D transmon qubits
Article metadata
Article Date: 05 November 2025
Article URL: https://www.nature.com/articles/s41586-025-09687-4
Article Image: (not provided)
Summary
This Nature paper reports millisecond-scale energy-relaxation (T1) and coherence (T2/Tphi) times in planar (2D) transmon qubits fabricated with high-quality tantalum (Ta) films on silicon. Key fabrication and materials-control steps — notably optimisation of Ta film growth and ultra-high-vacuum (UHV) junction deposition — produce devices with very high quality factors (Q ~9.8 × 10^6 on average) and qubits whose dephasing times improve dramatically when junctions are deposited in UHV rather than high vacuum. Material characterisation (STEM/EDS, XPS) shows clean Ta–Si interfaces with negligible intermixing or oxide contamination; resistivity and transition-temperature data confirm α-phase Ta (Tc ≈ 4.2 K). Device designs include Purcell-filtered readout so simulated Purcell-limited T1 exceeds 10 ms for the reported patterns. Across dozens of devices the authors report median T_phi ≈ 2.0 ms for UHV junction qubits versus ≈0.22 ms for HV junction qubits, and at least one qubit approaches the T2E = 2 T1 limit (T_phi ≈ 40 ms). Extensive extended data and tables give per-device T1, T2 and design parameters.
Key Points
- Demonstrated millisecond-scale lifetimes and coherence in 2D transmon qubits using Ta-on-Si fabrication.
- Ultra-high-vacuum (UHV) junction deposition greatly increases dephasing times: median T_phi ≈ 2.0 ms (UHV) vs 0.22 ms (HV).
- Average internal quality factor across devices is near 9.8 × 10^6, consistent with long T1 values.
- Careful materials characterisation shows a clean Ta–Si interface with no oxide intermixing and α-phase Ta (Tc ≈ 4.2 K).
- Device design includes Purcell filtering and simulated Purcell-limited T1 > 10 ms, indicating losses are dominated by materials/interfacial mechanisms rather than readout decay.
- Individual devices approach the T2E = 2 T1 limit; one qubit reported a T_phi ≈ 40 ms, showing decoherence can be moved far beyond typical values for planar transmons.
- Comprehensive extended data, tables and fabrication details are provided; raw data and analysis code are available from corresponding authors on request.
Context and relevance
Longer T1 and T2 times are critical for scaling superconducting processors and for reducing overheads in quantum error correction. Showing millisecond lifetimes in a 2D transmon architecture is important because 2D planar devices are simpler to manufacture and integrate than many 3D or more exotic designs; achieving ms coherence with standard planar layouts therefore lowers a materials-and-fabrication barrier to practical, larger-scale processors. The paper ties device performance to concrete fabrication choices (Ta growth, junction UHV deposition, trenching and design choices) and situates results alongside recent advances in coherence, error correction and device manufacturing. Researchers and engineers working on qubit materials, fabrication recipes, device layout or error-correction hardware will find the methods and per-device data immediately useful.
Why should I read this?
Short version: if you care about building real superconducting quantum hardware, this paper is proper gold. It proves you can hit millisecond lifetimes in a standard 2D transmon by nailing the materials and fabrication steps — not by exotic architectures alone. The write-up gives practical tweaks, per-device numbers and extended data so you can steal the good bits and try them in your lab. Basically: saves you months of trial-and-error by explaining what worked and why.
Source
Bland, M.P., Bahrami, F., Martinez, J.G.C. et al. Millisecond lifetimes and coherence times in 2D transmon qubits. Nature (2025). DOI: https://doi.org/10.1038/s41586-025-09687-4