Experimental Quantification of Asymmetric Einstein-Podolsky-Rosen Steering

Abstract

Einstein-Podolsky-Rosen (EPR) steering describes the ability of one observer to nonlocally "steer" the other observer's state through local measurements. EPR steering exhibits a unique asymmetric property, i.e., the steerability can differ between observers, which can lead to one-way EPR steering in which only one observer obtains steerability in the steering process. This property is inherently different from the symmetric concepts of entanglement and Bell nonlocality, and it has attracted increasing interest. Here, we experimentally demonstrate asymmetric EPR steering for a class of two-qubit states in the case of two measurement settings. We propose a practical method to quantify the steerability. We then provide a necessary and sufficient condition for EPR steering and clearly demonstrate one-way EPR steering. Our work provides new insight into the fundamental asymmetry of quantum nonlocality and has potential applications in asymmetric quantum information processing.Quantum nonlocality, which does not have a counterpart in classical physics, is the characteristic feature of quantum mechanics. First noted in the famous paper published by Einstein, Podolsky and Rosen (EPR) in 1935 [1], which aimed to argue the completeness of quantum mechanics, the content of quantum nonlocality has been greatly extended. In 2007, Wiseman et al. summarized the different conditions of quantum nonlocality and reformulated the concept of steering [2] originally introduced by Schrödinger [3] in response to the EPR paper (usually referred to as EPR steering), which stands between entanglement [1] and Bell nonlocality [4] in the hierarchy. In the view of a quantum information task, EPR steering can be regarded as the distribution of entanglement from an untrusted party, whereas entangled states need both parties to trust each other, and Bell nonlocality is presented on the premise that they distrust each other [5,6]. As a result, some entangled states cannot be employed to realize steering, and some steerable states do not violate Bell-like inequalities. EPR steering provides a novel insight into quantum nonlocality, and it exhibits an inherent asymmetric feature that differs from both entanglement and Bell nonlocality. Consider two observers, Alice and Bob, who share entangled states. There are cases in which the ability of Alice to steer Bob's state is not equal to the ability of Bob to steer Alice's state. There are also situations in which Alice can steer Bob's state but Bob cannot steer Alice's state, or vice versa; these situations are referred to as one-way steering [2,7]. Several * These two authors contributed equally to this work. theoretical [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] and experimental studies [23][24][25][26][27][28][29][30][31] have focused on the verification and applications of EPR steering. Experimental demonstrations of one-way steering with the measurements restricted to Gaussian measurements have been reported [24,25]. A class of entangled qubit states that can be used to show th...

Manipulation and enhancement of asymmetric steering via interference effects induced by closed-loop coupling

“…The steering strengths in two directions may not be the same [22], especially, a special type is known as one-way EPR steering where the entangled states show steering in one direction but not in the other [7,23]. The asymmetric EPR steering has attracted considerable attention recently for both theory [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] and experiment [14,23,[41][42][43][44][45][46]. One important method used in above studies to produce directional steering is making the states asymmetric by adding different amount of losses or noises on the subsystems.…”

Experimental observation of Einstein-Podolsky-Rosen steering via entanglement detection

“…The EPR steering of Gaussian states was verified by performing Gaussian measurements [29], and then was extended to a multipartite system [30]. By using the steering radius, Sun et al [31] and Xiao et al [32] explored the EPR steering in different directions through two-setting and multisetting projective measurements, respectively. The results show that the phenomenon of EPR steering may disappear with the increase of measurement setting in experiment.…”

Conclusive Experimental Demonstration of One-Way Einstein-Podolsky-Rosen Steering

“…Since the question whether one-way steering is possible was first raised in the seminal paper of Ref. [1], considerable progress has been made on the topic [2,4,[6][7][8][9][10][11][12][13][14][15][16][17]. Figure 1.…”