Qubits are made up of controlled particles and the means of control (e.g. devices that trap particles and switch them from one state to another). There are 4 established qubit candidates: ion traps, quantum dots, semiconductor impurities, and superconducting circuits.
adapted from Nanocomputers and Swarm Intelligence (page 157) ISTE, Waldner, JB (2007), ISBN 2746215160. Reproduced with author's authorization
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