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Quantum lower bound for inverting a permutation with advice

Abstract

Given a random permutation f:[N][N]f: [N] \to [N] as a black box and y[N]y \in [N], we want to output x=f1(y)x = f^{-1}(y). Supplementary to our input, we are given classical advice in the form of a pre-computed data structure; this advice can depend on the permutation but \emph{not} on the input yy. Classically, there is a data structure of size O~(S)\tilde{O}(S) and an algorithm that with the help of the data structure, given f(x)f(x), can invert ff in time O~(T)\tilde{O}(T), for every choice of parameters SS, TT, such that STNS\cdot T \ge N. We prove a quantum lower bound of T2SΩ~(ϵN)T^2\cdot S \ge \tilde{\Omega}(\epsilon N) for quantum algorithms that invert a random permutation ff on an ϵ\epsilon fraction of inputs, where TT is the number of queries to ff and SS is the amount of advice. This answers an open question of De et al. We also give a Ω(N/m)\Omega(\sqrt{N/m}) quantum lower bound for the simpler but related Yao's box problem, which is the problem of recovering a bit xjx_j, given the ability to query an NN-bit string xx at any index except the jj-th, and also given mm bits of advice that depend on xx but not on jj.

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