在这项工作中，我们引入了一个非线性见证，这是一个充分条件检测的量子关联的二分态的消失。我们的结果直接推广了[J.Maziero，R. M. Serra，arXiv：1012.3075]到任意维的基础上的Bloch表示的密度矩阵。
英文摘要：
In this work we introduce a nonlinear witness that is a sufficient condition for detecting the vanishment of quantum correlation of bipartite states. Our result directly generalizes the result of [J. Maziero, R. M. Serra, arXiv:1012.3075] to arbitrary dimension based on the Bloch representation of density matrices.
We provide a method for witnessing nonseparability of quantum processes on shared systems, which uses the channel-state duality. The method uses a maximally entangled state as a resource. We show that using the resource provides significant advantage over the corresponding protocol for nonseparability detection without the resource.
In a recent paper, Tilma, Everitt {\it et al.} derived a generalized Wigner function that can characterize both the discrete and continuous variable states, i.e., hybrid states. As such, one can expect that the negativity of the generalized Wigner function applied to the hybrid states can reveal their nonclassicality, in analogy with the well-known Wigner function defined for the continuous variable states. In this work, we demonstrate that, indeed, the negativity volume of the generalized Wigner function of the hybrid bipartite states can be used as an entanglement witness for such states, pr…
On witnessing arbitrary bipartite entanglement in a measurement device independent way
实验检测给定两体系统任意态的纠缠对于探索量子信息的许多领域是至关重要的。但是，如果认为态的制备过程是忠实的，则这种检测应该以与设备无关的方式进行，以避免将可分离态检测为纠缠态。最近开发的以独立于测量设备的方式检测二分纠缠的方案[Phys. Rev. Lett { \bf 110}，060405（2013）]确实需要关于状态的信息。在这里，通过使用Auguisiak et al.的两量子比特态的通用纠缠见证方案[Phys.Rev.A { \bf 77}，030301（2008）]，我们以测量设备无关的方式提供了一种两量子比特态的通用检测方案。我们提供了一套通用的证人运营商检测NPT-ness（负下部分转置）的状态在测量设备无关的方式。我们猜想对于PPT（positive under partial transpose）纠缠态，不存在这样一个普适的纠缠见证.我们还分析了一些实验方案的鲁棒性，这些实验方案在输入（来自裁判）以及参考文献[Phys. Rev. Lett { \bf 110}，060405（2013）]中设想的测量算子中的噪声的影响下，以独立于测量设备的方式检测纠缠。
Witness Operator Provides Better Estimate of the Lower Bound of Concurrence of Bipartite Bound Entangled States in $d_{1}\otimes d_{2}$ Dimensional System
In 2017 an idea considering a pair of Hermitian operators of product form was published, which is called ultrafine entanglement witnessing. In 2018 some rigorous results were given. Here we improve their work. First we point this idea can be directly derived from an earlier concept named joint separable numerical range and explain how it works as a series of witnesses. Second by a simple method we present a sufficient condition for an effective pair. Finally we prove this condition is necessary for optimization.
Entanglement detection problem is one of the important problem in quantum information theory. Gurvit showed that this problem is NP complete and thus this may be the possible reason that only one criterion is not sufficient to detect all entangled states. There are some powerful entanglement detection criterion such as partial transposition criterion, realignment criterion but it may not be possible to implement them successfully in the experiment. This situation can be avoided if the entanglement is detected through the construction of witness operator method. In this work, we take an analyti…
An entanglement witness is an observable detecting entanglement for a subset of states. We present a framework that makes an entanglement witness twice as powerful due to the general existence of a second (lower) bound, in addition to the (upper) bound of the very definition. This second bound, if non-trivial, is violated by another subset of entangled states. Differently stated, we prove via the structural physical approximation that two witnesses can be compressed into a single one. Consequently, our framework shows that any entanglement witness can be upgraded to a witness $2.0$. The genera…
Capturing specific kinds of quantum correlation is of paramount importance for quantum networking. Different routes can be taken to achieve this task, highlighting different novel aspects of such quantum correlations. Following the recent theoretical results by Yadin, Fadel and Gessner [Nat. Commun. 12, 2410 (2021)], we demonstrate experimentally how steering manifests in the metrological abilities of a bipartite state. Our results confirm the relevance of this novel approach, and compare the outcome with already employed alternatives.
Hardy's nonlocality argument as witness for post-quantum correlation
最近，Gallego等人[Phys. Rev. Lett 107，210403（2011）]证明了任何旨在区分量子和后量子关联的未来信息原理本质上必须是多部分的。利用三量子系统的Hardy非定域性论证的器件无关成功概率，我们得到了类似的结果。我们构造了一个三部Hardy关联的例子，它是后量子的，但不仅满足所有二部信息原理，而且还满足GYNI不等式。
Presence of correlations among the constituent quantum systems has a great relevance in thermodynamics. Significant efforts have been devoted to investigate the role of correlations in work extraction, among others. Here, we derive a bound on the difference between global and local extractable work by unitary operations (ergotropic gap), for bipartite separable states. Violation of this bound necessarily certifies the presence of entanglement. This gap is shown to be a monotone under LOCC assisted state transformations for pure bipartite quantum states. Our criterion has an implication in witn…
Quantum coherence has wide-ranging applications from quantum thermodynamics to quantum metrology, quantum channel discrimination and even quantum biology. Thus, detecting and quantifying coherence are two fundamental problems in quantum resource theory. Here, we introduce feasible methods to detect and estimate the coherence by constructing coherence witnesses for any finite-dimensional states. Our coherence witnesses detect coherent states by testing whether the expectation value of the witness is negative or not. Two typical coherence witnesses are proposed and discussed based on our witness…
