Superconducting Qubits

The most widely deployed qubit today — Josephson-junction circuits that behave as artificial atoms, operating in a dilution refrigerator.

In brief

• Built from Josephson junctions; the transmon is the dominant design.
• Operate at ~10–20 mK inside a dilution fridge.
• Fast gates (tens of ns) but relatively short coherence — error correction is essential.
• Used by several of the largest quantum-computing programs.

The detail

Superconducting qubits are lithographically fabricated circuits whose lowest two energy levels serve as |0⟩ and |1⟩. They are fast and manufacturable with semiconductor-style processes, which is why they anchor many large quantum roadmaps — but they demand deep cryogenics, tying the whole approach to helium-3 supply.