Determining Acceptance Possibility for a Quantum Computation is Hard for the Polynomial Hierarchy
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CitationFenner, Stephen; Green, Frederic; Homer, Steven; Pruim, Randall. "Determining Acceptance Possibility for a Quantum Computation is Hard for the Polynomial Hierarchy", Technical Report BUCS-2000-002, Computer Science Department, Boston University, January 20, 2000. [Available from: http://hdl.handle.net/2144/1797]
It is shown that determining whether a quantum computation has a non-zero probability of accepting is at least as hard as the polynomial time hierarchy. This hardness result also applies to determining in general whether a given quantum basis state appears with nonzero amplitude in a superposition, or whether a given quantum bit has positive expectation value at the end of a quantum computation. This result is achieved by showing that the complexity class NQP of Adleman, Demarrais, and Huang, a quantum analog of NP, is equal to the counting class coC=P.