Complexity limitations on quantum computation

Abstract

We use the powerful tools of counting complexity and generic oracles to help understand the limitations of the complexity of quantum computation. We show several results for the probabilistic quantum class BQP: BQP is low for PP, i.e., PPBQP = PP; There exists a relativized, world, where P = BQP and the polynomial-time hierarchy is infinite; There exists a relativized world, where BQP does not have complete sets; There exists a relativized world, where P = BQP, but P≠UPqqcoUP and one-way functions exist. This gives a relativized answer to an open question of Simon.