NQP = co-C=P

Adleman, Demarrais, and Huang introduced the nondeterministic quantum polynomial-time complexity class NQP as an analogue of NP. It is known that, with restricted amplitudes, NQP is characterized in terms of the classical counting complexity class C=P. In this paper we prove that, with unrestricted amplitudes, NQP indeed coincides with the complement of C=P. As an immediate corollary, with unrestricted amplitudes BQP differs from NQP. key words: computational complexity, theory of computation

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