In quantum computing, the (quantum) threshold theorem (or quantum fault-tolerance theorem), proved by Michael Ben-Or and Dorit Aharonov (along with other groups), states that a quantum computer with noise can quickly and accurately simulate an ideal quantum computer, provided the level of noise is below a certain threshold. Practically, the Threshold Theorem implies that the error in quantum computers can be controlled as the number of qubits scales up.
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Quantum threshold theorem Wikipedia(Text) CC BY-SA