The General Adversary Bound: A Survey

Abstract

Ben Reichardt showed in a series of results that the general adversary bound of a function characterizes its quantum query complexity. This survey seeks to aggregate the background and definitions necessary to understand the proof. Notable among these are the lower bound proof, span programs, witness size, and semi-definite programs. These definitions, in addition to examples and detailed expositions, serve to give the reader a better intuition of the graph-theoretic nature of the upper bound. We also include an applications of this result to lower bounds on DeMorgan formula size.