Polynomial interpolation from oracle queries

ALGORITHM: Polynomial interpolation from oracle queries
PROBLEM: Given an oracle that returns the value p(x) of an unknown degree-d polynomial p over the finite field GF(q) at any queried point x, determine the coefficients of p using as few queries as possible.
IDEA: Classically the d + 1 coefficients cannot be pinned down with fewer than d + 1 queries, and a lower bound proved independently by Kane and Kutin and by Meyer and Pommersheim puts the quantum cost at d/2 + 1/2 queries. Childs, van Dam, Hung and Shparlinski describe an algorithm that attains that lower bound rather than the d queries of the earlier Boneh and Zhandry algorithm, and they show that its success probability, as a function of the number of queries, is precisely optimal. Their abstract states that the algorithm can be implemented with gate complexity poly(log q) with negligible decrease in the success probability. Chen, Childs and Hung carry the same question to a degree-d polynomial in n variables, where their abstract reports a speedup over the classical count (n+d choose d) by a factor of n+1 over ℂ, (n+1)/2 over ℝ and (n+d)/d over GF(q), which it calls a much larger gap than the factor of 2 available in the univariate case.
REPORTED COST: Univariate over GF(q): d/2 + 1/2 quantum queries suffice to determine a degree-d polynomial with bounded error, which matches the lower bound, and d/2 + 1 queries suffice for success probability approaching 1 at large q, against d + 1 queries necessary and sufficient classically; the algorithm can be implemented with gate complexity poly(log q) with negligible decrease in the success probability. Multivariate, for degree d in n variables: ⌈(1/(n+1))·(n+d choose d)⌉ queries suffice for probability 1 over ℂ and twice that over ℝ, except for d = 2 and four other special cases, and ⌈(d/(n+d))·(n+d choose d)⌉ queries suffice for probability approaching 1 over GF(q) at large field order, against a classical query complexity of (n+d choose d).
BASIS: abstract of arXiv:1509.09271: "A lower bound shown independently by Kane and Kutin and by Meyer and Pommersheim shows that d/2+1/2 quantum queries are needed to solve this problem with bounded error, whereas an algorithm of Boneh and Zhandry shows that d quantum queries are sufficient. We show that the lower bound is achievable: d/2+1/2 quantum queries suffice to determine the polynomial with bounded error. Furthermore, we show that d/2+1 queries suffice to achieve probability approaching 1 for large q", and "the algorithm can be implemented with gate complexity poly(log q) with negligible decrease in the success probability". The classical univariate count is from the Quantum Algorithm Zoo entry "Polynomial interpolation" (LaTeX rendered into plain text): "Classically, d + 1 queries are necessary and sufficient." The multivariate figures are from the abstract of arXiv:1701.03990, with TeX rendered into Unicode, the binomial written as (n+d choose d) and the subscript of k written as C rather than ℂ: "We show that k_C and 2k_C queries suffice to achieve probability 1 for ℂ and ℝ, respectively, where k_C=⌈(1/(n+1))(n+d choose d)⌉ except for d=2 and four other special cases. For 𝔽_q, we show that ⌈(d/(n+d))(n+d choose d)⌉ queries suffice to achieve probability approaching 1 for large field order q", and "The classical query complexity of this problem is (n+d choose d), so our result provides a speedup by a factor of n+1, (n+1)/2, and (n+d)/d for ℂ, ℝ, and 𝔽_q, respectively." Outside the quotations the finite field is written GF(q) throughout, as in the Zoo entry; the multivariate paper writes the same field as a blackboard-bold F with subscript q, and the Zoo states the multivariate quantum counts in O(·) form rather than as the paper's ceilings.
PRIMARY SOURCE: Andrew M. Childs, Wim van Dam, Shih-Han Hung, Igor E. Shparlinski (2015), Optimal quantum algorithm for polynomial interpolation — https://arxiv.org/abs/1509.09271

This is a literature reference record, not an executable circuit.