Aluminum Oxide (AlOx) Tunnel Barrier¶
Superconducting Materials
The Quantum Tunneling Element — Heart of the Josephson Junction
Non-superconducting amorphous dielectric (~1–3 nm)
Aluminum Oxide (AlOx) Tunnel Barrier¶
The Quantum Tunneling Element — Heart of the Josephson Junction
Role in quantum circuits
Insulating tunnel barrier in Al/AlOx/Al Josephson junctions — defines qubit nonlinearity
Why it matters
- The AlOx tunnel barrier is the most critical element in superconducting qubits. Formed
by controlled thermal oxidation of aluminum, it creates a ~1–2 nm amorphous oxide through which Cooper pairs tunnel, producing the non-linear inductance that makes a qubit distinct from a classical LC oscillator.
Key facts
Formed by controlled O₂ exposure of Al surface (thermal oxidation)
Thickness (~1–2 nm) sets the critical current Ic of the junction
Amorphous structure introduces TLS defects — primary decoherence source
Shadow-angle evaporation produces self-aligned Josephson junctions
Cleaner barriers can extend (T_1) coherence times