Universal quantum computation with little entanglement

Abstract

We show that universal quantum computation can be achieved in the standard pure-state circuit model while, at any time, the entanglement entropy of all bipartitions is small---even tending to zero with growing system size. The result is obtained by showing that a quantum computer operating within a small region around the set of unentangled states still has universal computational power, and by using continuity of entanglement entropy. In fact an analogous conclusion applies to every entanglement measure which is continuous in a certain natural sense, which amounts to a large class. Other examples include the geometric measure, localizable entanglement, smooth epsilon-measures, multipartite concurrence, squashed entanglement, and several others. We discuss implications of these results for the believed role of entanglement as a key necessary resource for quantum speed-ups.