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Glossary / Quantum computing

Quantum computer

A computer that calculates using quantum-mechanical properties such as superposition and entanglement. It is expected to solve certain kinds of problem far faster than ordinary computers.

In 1982 Richard Feynman pointed out that calculating the behaviour of quantum systems on an ordinary computer becomes explosively harder as particles are added, and proposed letting a machine that itself runs on quantum rules do the work[1]. In 1985 David Deutsch defined a universal quantum computer, one able to carry out any quantum computation[2].

Its strengths lie in a limited set of problems, such as simulating molecules and materials or factoring large numbers. It does not speed up every calculation. Qubits are also fragile, and useful-scale computations need error correction. The current contest among companies is over whether that error correction can be kept running on real hardware.

Related terms

  • QubitThe basic unit of information in a quantum computer. Rather than being either 0 or 1, it can be in a superposition of both.
  • Quantum error correctionSpreading the information of fragile qubits across many of them, so that errors can be detected and fixed.
  • Quantum advantageThe point at which a quantum computer solves some computational problem faster than the best classical computer can.

Sources

  1. R. P. Feynman, “Simulating physics with computers,” Int. J. Theor. Phys. 21, 467–488 (1982).
  2. D. Deutsch, “Quantum theory, the Church–Turing principle and the universal quantum computer,” Proc. R. Soc. Lond. A 400, 97–117 (1985).