Polynomial degree vs. quantum query complexity

Andris Ambainis

Abstract: The degree of a polynomial representing (or approximating) a function f is a lower bound for the quantum query complexity of f. This observation has been a source of many lower bounds on quantum algorithms. It has been an open problem whether this lower bound is tight.We exhibit a function with polynomial degree M and quantum query complexity Ω(M1.321…). This is the first superlinear separation between polynomial degree and quantum query complexity. The lower bound is shown by a generalized version of the quantum adversary method.