How many mutually unbiased bases are needed to detect bound entangled states?

Abstract

From a practical perspective it is advantageous to develop methods that verify entanglement in quantum states with as few measurements as possible. In this paper we investigate the minimal number of mutually unbiased bases (MUBs) needed to detect bound entanglement in bipartite (dxd)-dimensional states, i.e. entangled states that are positive under partial transposition. In particular, we show that a class of entanglement witnesses (EWs) composed of MUB scan detect bound entanglement if the number of measurements is greater than d/2+1. This is a substantial improvement over other detection methods, requiring significantly fewer resources than either full quantum state tomo-graphy or measuring a complete set ofd+1 MUBs. Our approach is based ona partial characterisation of the (non-)decomposability of EWs. We show that non-decomposability is a universal property of MUBs, which holds regardless of the choice of complementary observables, and we find that both the number of measurements and the structure of the witness play an important role in the detection of bound entanglement.