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This class is defined for a quantum computer and its natural corresponding class for an ordinary computer ( or a Turing machine plus a source of randomness ) is BPP.

Just like P and BPP, BQP is low for itself, which means BQP < sup > BQP </ sup > = BQP.

Informally, this is true because polynomial time algorithms are closed under composition.

If a polynomial time algorithm calls as a subroutine polynomially many polynomial time algorithms, the resulting algorithm is still polynomial time.