The design and theory of computer systems that depend on quantum effects for their operation. On one level, this can be the use of small components, at the atomic or molecular level, to store or process information. An example would be a storage system that used two different spin states of atoms to store bits of information, or a logic gate that depends on the movement or spin of a single electron. Systems of this type are studied in nanocomputing (see also spintronics). At a more fundamental level, the term ‘quantum computing’ implies the use of quantum effects that have no classical analogue to process information. In a ‘classical’ computer information is held in bits, which can have two alternative values (0 and 1). In a quantum computer the 0 and 1 values are held simultaneously in an entangled state. This unit of information is a quantum bit (or qubit). Much more information can be held in this way and, in principle, it is possible to do parallel processing of the information. Quantum computers would be much faster than conventional machines and capable of performing calculations that could not realistically be done otherwise. Ion traps, cavity QED, and spin measurements have been used in research in this area. See also Quantum Entanglement (Feature).

https://www.wired.com/2014/05/quantum-computing/ Article on the history of research into quantum computing