Stoquastic acceptance floor
= Stoquastic acceptance floor
{title2=$p_+\geq1/2$}
If the output of a <stoquastic circuit> is $|0\rangle|r_0\rangle+|1\rangle|r_1\rangle$ with nonnegative amplitudes, its plus-outcome probability is $1/2+\operatorname{Re}\langle r_0|r_1\rangle\geq1/2$. Basis <quantum witnesses> with zero and plus <ancilla qubits> always have this property. A soundness threshold below one half cannot hold for every such input.