A Note on Oracle Separations for BQP

Abstract

In 2009, using the $\textsf{Fourier Checking}$ problem, Aaronson claimed to construct the relativized worlds such that $\textsf{BQP} \not\subset \mathsf{BPP_{path}}$ and $\textsf{BQP} \not\subset \textsf{SZK}$. However, there are subtle errors in the original proof. In this paper, we point out the issues, and rescue these two separations by using more sophisticated constructions. Meanwhile, we take the opportunity to study the complexity classes $\mathsf{BPP_{path}}$ and $\textsf{SZK}$. We give general ways to construct functions which are hard for $\textsf{SZK}$ and $\mathsf{BPP_{path}}$ (in the query complexity sense). Using these techniques, we give alternative construction for the oracle separation $\textsf{BQP} \not\subset \textsf{SZK}$, using only Simon's problem. We also give new oracle separations for $\textsf{P}^{\textsf{SZK}}$ from $\mathsf{BPP_{path}}$ and $\textsf{P}^{\textsf{SZK}}$ from $\textsf{QSK}$. The latter result suggests that $\textsf{P}^{\textsf{SZK}}$ might be strictly larger than $\textsf{SZK}$.