Glossary / Quantum computing
Qubit
The basic unit of information in a quantum computer. Rather than being either 0 or 1, it can be in a superposition of both.
A classical bit is either 0 or 1. A qubit can be in a superposition of the two, and when several qubits are entangled the whole set of combinations can be handled at once. That is where a quantum computer's power comes from. The name "qubit" first appeared in a 1995 paper by Benjamin Schumacher[1].
The weakness is fragility. A little heat or electromagnetic noise destroys the superposition, so the real, physical qubits accumulate errors quickly if used directly. Bundling them together to protect the information is the job of error correction and logical qubits.
Related terms
- Logical qubitA single, robust qubit made by bundling many physical qubits together and running error correction on them.
- Superconducting qubitA qubit made from a superconducting circuit, which has zero electrical resistance at very low temperature. Used by IBM, Google, Fujitsu and others.
- Trapped ionUsing atomic ions, suspended in a vacuum by electric fields and manipulated with lasers, as qubits. Used by Quantinuum and others.