Aluminum Oxide (AlOx) Tunnel Barrier
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**Superconducting Materials**

The Quantum Tunneling Element — Heart of the Josephson Junction

**Non-superconducting amorphous dielectric (~1–3 nm)**

Aluminum Oxide (AlOx) Tunnel Barrier
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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