Superconducting qubits
Chip-based qubits cooled to near absolute zero. The current front-runner.
Superconducting qubits are tiny electrical circuits printed on a chip that behave quantum-mechanically when chilled to about 15 millikelvin — colder than deep space. They switch extremely fast and are built with adapted semiconductor manufacturing, which is why IBM, Google, Rigetti and others have pushed them furthest.
In plain terms
Think of a child's swing that can somehow swing forwards and backwards at the same time. The superconducting circuit is that swing; microwave pulses are the gentle pushes that steer it. Everything has to be kept perfectly still (and freezing) or the motion blurs away.
How it works
The heart of the qubit is a Josephson junction — two superconductors separated by a thin barrier — which makes an electrical circuit whose energy levels are unevenly spaced. That lets engineers isolate the lowest two levels as the 0 and 1.
Qubits are controlled and read out with precisely shaped microwave pulses, and the whole chip sits at the bottom of a dilution refrigerator — the iconic gold 'chandelier'.
Because gates are very fast (nanoseconds), lots of operations fit inside the short time before the qubit decoheres. The trade-off is that qubits only talk to their near neighbours, so connectivity and crosstalk are ongoing challenges.
The problem it solves
Superconducting systems are the most mature path to a large, fast, gate-based quantum computer, leveraging existing chip fabs. They aim squarely at chemistry, optimization and, eventually, error-corrected general-purpose quantum computing.
- +Very fast gate speeds; huge operation budget per coherence window.
- +Made with adapted semiconductor fabrication — a clear path to scale.
- +Best-funded, most-demonstrated modality to date.
- –Requires dilution refrigerators near absolute zero.
- –Limited qubit connectivity and crosstalk between neighbours.
- –Coherence times are shorter than trapped ions.
Companies building this
Builds its own superconducting chips in-house and delivers them via the cloud — vertical integration for faster iteration.
Europe's superconducting champion, delivering on-premises systems to HPC centres for sovereignty and integration.
Uses bosonic error correction to cut the number of physical qubits needed per logical qubit.