Einstein-Podolsky-Rosen Steering in Two-sided Sequential Measurements with One Entangled Pair

Abstract

Non-locality and quantum measurement are two fundamental topics in quantum theory and their interplay attracts intensive focuses since the discovery of Bell theorem. Recently, non-locality sharing among multiple observers with one entangled pair has been predicted and experimentally observed by generalized quantum measurement -weak measurement. However, only one-sided sequential case, i.e., one Alice and multiple Bobs is widely discussed and little is known about the two-sided case.Here, we theoretically and experimentally explore the non-locality sharing in two-sided sequential measurements case in which one entangled pair is distributed to multiple Alices and Bobs. We experimentally observed double EPR steering among four observers in a photonic system. In the case that all observers adopt the same measurement strength of the weak measurement, it is observed that double EPR steering can be demonstrated simultaneously. The results not only deepen our understanding of relation between sequential measurements and non-locality but also may find important applications in many quantum information tasks, such as randomness certification.

Recycled entanglement detection by arbitrarily many sequential and independent pairs of observers

“…It is found that an arbitrary number of pairs of sequential and independent observers can witness entanglement, acting locally on two-qubit entangled states. This result is potentially of importance, given that it has been conjectured that not more than a single pair of observers can detect CHSH Bell-nonlocal correlations in the same scenario [37][38][39]. Assuming that the conjecture in the literature is true, our finding demonstrates a clear distinction between "entanglement nonlocality" and "Bell nonlocality", with respect to sequential witnessing by pairs of observers.…”

“…Recently, it was also observed that it is possible to witness and recycle entanglement an arbitrary number of times using a CHSH Bell-local entangled state [26]. For other theoretical works in the direction of recyclability of entangled and nonlocal correlations, see [27][28][29][30][31][32][33][34][35][36][37][38][39][40]. For experimental works, see [41][42][43][44][45].…”

“…In the present work, we consider the scenario in which both the subsystems of a bipartite quantum state are passed on to multiple pairs of independent observers [37][38][39][40]. See Fig.…”

Network nonlocality sharing via weak measurements in the extended bilocal scenario

“…when θ 1,0 = θ 1,1 = π 4 for Alice [48,49]. In particular, network nonlocal sharing can also be divided into two different types of nonlocality sharing, passive and active network nonlocal sharing, according to the different motivations of the former observers Alice 1 and Charlie 1 .…”

“…Nonlocal sharing has attracted extensive attention [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50], and lots of relevant results have been published ever since, such as active and passive nonlocal sharing [35], quantum steering sharing [47] and so on. However, almost all discussions are limited to the case of one-sided sequential measurements, that is, an entangled pair is distributed to one Alice and multiple [48,49]. Such discrepancy may give a hint to exhibit the different properties between network nonlocality and Bell nonlocality.…”