Dagomir Kaszlikowski, Darwin Gosal, E. J. Ling, L. C. Kwek, Marek Zukowski, C. H. Oh
We present numerical data showing, that three qutrit correlations for a pure state, which is not maximally entangled, violate local realism more strongly than three-qubit correlations. The strength of violation is measured by the minimal amount of noise that must be admixed to the system so that the noisy correlations have a local and realistic model.
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Greenberger-Horne-Zeilinger (GHZ) paradox provides an all-versus-nothing test for the quantum nonlocality. In all the GHZ paradoxes known so far each observer is allowed to measure only two alternative observables. Here we shall present a general construction for GHZ paradoxes in which each observer measuring more than two observables given that the system is prepared in the $n$-qudit GHZ state. By doing so we are able to construct a multi-setting GHZ paradox for the $n$-qubit GHZ state, with $n$ being arbitrary, that is genuine $n$-partite, i.e., no GHZ paradox exists when restrict to a subse…
One fascinating way of revealing the quantum nonlocality is the all-versus-nothing test due to Greenberger, Horne, and Zeilinger (GHZ) known as GHZ paradox. So far genuine multipartite and multilevel GHZ paradoxes are known to exist only in systems containing an odd number of particles. Here we shall construct GHZ paradoxes for an arbitrary number (greater than 3) of particles with the help of qudit graph states on a special kind of graphs, called as GHZ graphs. Based on the GHZ paradox arising from a GHZ graph, we derive a Bell inequality with two $d$-outcome observables for each observer, wh…
Stronger Nonlocality in GHZ States: A Step Beyond the Conventional GHZ Paradox
本文提出随机化变体GHZ博弈，通过随机选取承诺条件并仅披露给随机一方，证明其可由GHZ态完美求解，展现出更强的非定域性，且在分布式多体通信复杂度任务中具备更大通信优势。
We construct GHZ contradictions for three or more parties sharing an entangled state, the dimension d of each subsystem being an even integer greater than 2. The simplest example that goes beyond the standard GHZ paradox (three qubits) involves five ququats (d=4). We then examine the criteria a GHZ paradox must satisfy in order to be genuinely M-partite and d-dimensional.
Quatum nonlocality as a valuable resource is of vital importance in quantum information processing. The characterization of the resource has been extensively investigated mainly for pure states, while relatively less is know for mixed states. Here we prove the existence of the optimal GHZ paradox by using a novel and simple method to extract an optimal state that can saturate the tradeoff relation between quantum nonlocality and the state purity. In this paradox, the logical inequality which is formulated by the GHZ-typed event probabilities can be violated maximally by the optimal state for a…
Experimental Test of Irreducible Four-Qubit Greenberger-Horne-Zeilinger Paradox
本研究提出不可约的四量子比特Greenberger-Horne-Zeilinger（GHZ）悖论并完成实验演示，填补了此前多量子比特GHZ悖论检验可约化为三比特的可约性漏洞，实验观测到Bell-GHZ不等式7σ违反及纠缠见证19σ的可分阈值违反。
We present probabilistic analysis of the Greenberger-Horne-Zeilinger (GHZ) scheme in the contextualist framework, namely under the assumption that distributions of hidden variables depend on settings of measurement devices. On one hand, we found classes of probability distributions of hidden variables for that the GHZ scheme does not imply a contradiction between the local realism and quantum formalism. On the other hand, we found classes of probability distributions of hidden variables for that the GHZ scheme still induce such a contradiction (despite variations of distributions). It is also …
The Greenberger-Horne-Zeilinger~(GHZ) version of the Einstein-Podolsky-Rosen~(EPR) paradox is widely regarded as a conclusive logical argument that rules out the possibility of describing quantum phenomena within the framework of a local and realistic model of hidden variables in which the observers are free to choose their own experimental settings. In this paper we show, however, that the GHZ argument implicitly relies on an additional crucial assumption, which is not required by fundamental physical principles and had gone unnoticed. Namely, we note that the argument implicitly assumes the …
A refined Frauchiger--Renner paradox based on strong contextuality
本文通过识别逻辑语境性（Hardy 型）是 Frauchiger-Renner 悖论的关键要素，并基于强语境性的 GHZ-Mermin 场景提出了一个更强的悖论（GHZ-FR 悖论），该悖论无需后选择或量子建模观察者的推理。
In quantum theory, no-go theorems are important as they rule out the existence of a particular physical model under consideration. For instance, the Greenberger-Horne-Zeilinger (GHZ) theorem serves as a no-go theorem for the nonexistence of local hidden variable models by presenting a full contradiction for the multipartite GHZ states. However, the elegant GHZ argument for Bell's nonlocality does not go through for bipartite Einstein-Podolsky-Rosen (EPR) state. Recent study on quantum nonlocality has shown that the more precise description of EPR's original scenario is "steering", i.e., the no…
Three-qubit nonlocality paradoxes: beyond GHZ
本文通过引入新的结构和组合技术，完全分类了基于双条件奇偶性证明的三量子比特非局域性悖论，揭示了比先前理解更丰富的悖论景观。
Hardy-type self-testing and exposedness of tripartite GHZ correlations
研究三体两输入两输出场景中Hardy型悖论的自检验，证明最大Hardy成功概率关联自检验GHZ态和测量，且该关联是量子关联集的极点和暴露点，与Mermin不等式最大违反点重合。
How common is large-scale entanglement in nature? As a first step towards addressing this question, we study the robustness of multi-party entanglement under local decoherence, modeled by partially depolarizing channels acting independently on each subsystem. Surprisingly, we find that n-qubit GHZ entanglement can stand more than 55 % local depolarization in the limit of n going to infinity, and that GHZ states are more robust than other generic states of 3 and 4 qubits. We also study spin-squeezed states in the limit n going to infinity and find that they too can stand considerable local depo…
An Einstein-Podolsky-Rosen argument based on weak forms of local realism not falsifiable by GHZ or Bell experiments
本文提出基于弱形式局域实在论的EPR论证，其前提无法被GHZ或贝尔实验证伪；设计宏观EPR/GHZ实验，结合弱宏观实在论（wMR）仍能产生EPR悖论，重新审视原始EPR悖论也得出类似结论。
We present a generalized Greenberger-Horne-Zeilinger (GHZ) theorem, which involves more than two local measurement settings for some parties, and cannot be reduced to one with less settings. Our results hold for an odd number of parties. We use a set of observables, which are incompatible but share a common eigenstate, here a GHZ state. Such observables are called concurrent. The idea is illustrated with an example of a three-qutrit system and then generalized to systems of higher dimensions, and more parties. The GHZ paradoxes can lead to, e.g., secret sharing protocols.
Exploring the boundary of quantum correlations with a time-domain optical processor
本文推导出语境覆盖数为3且达到量子理论下界的GHZ型悖论，并通过时域光纤光学平台在37维装置中成功演示，为利用时分复用光学系统探索高维量子关联铺平了道路。
The Greenberger-Horne-Zeilinger (GHZ) effect provides an example of quantum correlations that cannot be explained by classical local hidden variables. This paper reports on the experimental realization of GHZ correlations using nuclear magnetic resonance (NMR). The NMR experiment differs from the originally proposed GHZ experiment in several ways: it is performed on mixed states rather than pure states; and instead of being widely separated, the spins on which it is performed are all located in the same molecule. As a result, the NMR version of the GHZ experiment cannot entirely rule out class…
Going beyond the entanglement of microscopic objects (such as photons, spins, and ions), here we propose an efficient approach to produce and control the quantum entanglement of three macroscopic coupled superconducting qubits. By conditionally rotating, one by one, selected Josephson charge qubits, we show that their Greenberger-Horne-Zeilinger (GHZ) entangled states can be deterministically generated. The existence of GHZ correlations between these qubits could be experimentally demonstrated by effective single-qubit operations followed by high-fidelity single-shot readouts. The possibility …
A measure for genuine tripartite entanglement
提出一个基于四个三量子比特关联期望值的实值泛函，将GHZ代数悖论转化为真正三方纠缠的定量判据，并证明其最大值为2，仅在GHZ态时达到。
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