Sequentially witnessing entanglement by independent observer pairs

Abstract

This study delves into measurement strategies within a scenario where multiple pairs of Alices and Bobs independently and sequentially observe entangled states. The goal is to maximize the number of observer pairs (Ak,Bl) capable of witnessing entanglement. Previous research has shown that arbitrary pairs (Ak,Bk) (k≤n) can detect entanglement in all pure entangled states and a specific class of mixed entangled states [Pandit et al. (2022) [37]]. However, it's worth noting that other pairs (Ak,Bl) with (k≠l≤n) may not observe entanglement using the same method. Additionally, a novel strategy is introduced, allowing every pair of arbitrarily many Alices and Bobs to witness entanglement regardless of whether the initial state is a Bell state or a particular class of mixed entangled states. These findings contribute to our understanding of measurement strategies aimed at maximizing entanglement observation in various contexts.