J. Silman, B. Reznik
The correlations between three arbitrarily far-apart regions of the vacuum state of the free Klein-Gordon field are investigated by means of its finite duration coupling to three localized detectors. It is shown that these correlations cannot be reproduced in terms of a hybrid local-nonlocal hidden-variable model, i.e., the correlations between three arbitrarily separated regions of the vacuum are fully nonlocal.
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Transfer of nonlocal two-mode squeezed vacuum state through symmetrical and asymmetrical lossy channel is analysed and we demonstrate that the nonlocality is more robust against losses, than it has been previously suggested. It can be important for security of continuous-variable quantum cryptography employing entangled states.
We propose a single-particle experiment that is equivalent to the conventional two-particle experiment used to demonstrate a violation of Bell's inequalities. Hence, we argue that quantum mechanical nonlocality can be demonstrated by single-particle states. The validity of such a claim has been discussed in the literature, but without reaching a clear consensus. We show that the disagreement can be traced to what part of the total state of the experiment one assigns to the (macroscopic) measurement apparatus. However, with a conventional and legitimate interpretation of the measurement process…
Experimental hierarchy of the nonclassicality of single-qubit states via potentials for entanglement, steering, and Bell nonlocality
本研究将纠缠势概念推广至EPR导引和贝尔非局域性以研究非经典性层级，并利用偏振编码单光子态进行实验验证，该方法无需真空检测，实验上更为便捷。
Quantum entanglement is the quintessential characteristic of quantum mechanics and the basis for quantum information processing. When one of two maximally entangled particles is measured, without measurement the state of another one is determined simultaneously no matter how far the two particles is from each other. How can these phenomena take place since no object can move faster than light speed in a vacuum? The key problem is due to the ignorance of the interaction between a particle and a quantum vacuum. Just like the case where a gun suffers recoil from its firing of a bullet, when a par…
Quantifying nonclassicality of vacuum-one-photon superpositions via potentials for Bell nonlocality, quantum steering, and entanglement
本文将纠缠势推广为贝尔非定域性势和量子导引势，并以真空-单光子叠加态为例，系统研究了单模非经典性的层级结构及实验实现和误差影响。
Dynamical Casimir Effects: The Need for Nonlocality in Time-Varying Dispersive Nanophotonics
本文研究了时变色散纳米光子系统动力学 Casimir 效应中材料的非局域性，指出局域模型会导致纠缠极化子对发射率发散等非物理预测，而非局域性可正则化该行为并揭示发射率分布展宽等局域模型遗漏的物理效应。
We develop dynamical non-Markovian description of quantum computing in weak coupling limit, in lowest order approximation. We show that long range memory of quantum reservoir produces strong interrelation between structure of noise and quantum algorithm, implying nonlocal attacks of noise. We then argue that the quantum error correction method fails to protect quantum computation against electromagnetic or phonon vacuum which exhibit $1/t^4$ memory. This shows that the implicit assumption of quantum error correction theory -- independence of noise and self-dynamics -- fails in long time regime…
Bell Nonlocality Test on Two-Mode Squeezed Output Generated in Double-Cavity Optomechanical
研究通过共振工程在双腔声光机械系统中生成双模压缩输出，探讨压缩与非局域性之间的关系，发现非局域性可在低压缩状态下出现，且高精细度参数区域可扩大非局域性支持区域。
In the quest for an understanding of nonlocality with respect to an appropriate ontology, we propose a "cosmological solution". We assume that from the beginning of the universe each point in space has been the location of a scalar field representing a zero-point vacuum energy that nonlocally vibrates at a vast range of different frequencies across the whole universe. A quantum, then, is a nonequilibrium steady state in the form of a "bouncer" coupled resonantly to one of those (particle type dependent) frequencies, in remote analogy to the bouncing oil drops on an oscillating oil bath as in C…
Nonlocal correlations are a central feature of quantum theory, and understanding why quantum theory has a limited amount of nonlocality is a fundamental problem. Since nonlocality also has technological applications, e.g., for device-independent cryptography, it is useful to understand it as a resource and, in particular, whether and how different types of nonlocality can be interconverted. Here we focus on nonlocality distillation which involves using several copies of a nonlocal resource to generate one with more nonlocality. We introduce several distillation schemes which distil an extended…
We analyze nonclassical correlations between outcomes of measurements conducted on two spatial radiation modes. These correlations cannot be simulated with statistical mixtures of coherent states or, more generally, with non-negative phase-space functions of quantum states and measurements. We argue that nonclassical correlations are naturally related to Bell nonlocality, the former being a more general class of quantum correlations. Indeed, it is known that local realistic as well as noncontextual models correspond to non-negative solutions to a system of linear equations for the joint probab…
Transfer of nonlocality and entanglement of an open three-qubit W state in the background of dilaton black hole
研究开放三粒子W态在稀顿黑洞背景下的非局域性和纠缠特性，探讨环境退相干和时空稀顿对三粒子非局域性和真实三粒子纠缠的影响，发现非局域性和纠缠在物理可及区域的行为差异。
Incompatibility assisted Zeno-like confinement enables unbounded sharing of nonlocality
研究无界数量副本顺序共享贝尔非局域性的条件，通过不相容测量提取非局域性，后处理态保持非局域，建立两种测量场景下初始态和测量噪声选择的约束，证明渐近极限下副本后处理态近似相同。
Quantum correlations of tripartite mixed states in the black hole quantum atmosphere
研究黑洞量子大气中三方混合态的量子关联，通过引入哈特尔 - 霍金局部温度刻画局部霍金效应影响，发现相关量极值在近视界区域，且三方非定域性更脆弱，为三方混合态相关特性提供统一刻画。
Bell nonlocality and entanglement in $e^{+}e^{-} \rightarrow Y\bar{Y}$ at BESIII
本文提出一种系统方法研究BESIII中正负电子湮灭产生的自旋1/2超子-反超子系统的量子关联，发现其非定域性运动学区域比$τ^{+}τ^{-}$系统更受限，并给出了探测实验方案。
The experimental results that test Bell's inequality have found strong evidence suggesting that there are nonlocal aspects in nature. Evidently, these nonlocal effects, which concern spacelike separated regions, create an enormous tension between general relativity and quantum mechanics. In addition, by avoiding the coincidence limit, semiclassical gravity can also accommodate nonlocal aspects. Motivated by these results, we study if it is possible to construct geometrical theories of gravitation that are nonlocal in the sense of Bell. We propose three constructions of such theories, which cou…
Entanglement Harvesting from Electromagnetic Quantum Fields
提出基于电光采样（EOS）的纠缠提取实验方案，证明其能从真空场提取纠缠并探测Bell非定域性，同时引入减轻散粒噪声的新方法，推动相对论量子场论与太赫兹量子光学研究。
Nonlocal Static and Dynamical Vacuum Field Correlations and Casimir-Polder Interactions
本综述研究无质量标量场和电磁场在静态与非静态条件下的空间场关联的非局域特征，及其在范德瓦尔斯和卡西米尔-波尔德相互作用中的体现，并探讨了通过原子间作用间接探测真空场关联的可能性。
There are two main approaches to generate the negative energy density (NED) in the literature. The Casimir effect and the squeezed vacuum. The possibility of the latter approach is qualitatively reviewed in this paper. It is proposed that the soliton theory may give remarkable contributions to generate and separate the NED out of the quantum vacuum. By applying the wavelength-division multiplexing (WDM) method on the solitonized laser beams which give rise the squeezed regions of the vacuum, it is shown the solitons' properties can be useful to the chosen approach.
We investigate the correlations between any number of arbitrarily far-apart regions of the vacuum of the free Klein-Gordon field by means of its finite duration coupling to an equal number of localized detectors. We show that the correlations between any N such regions enable us to distill an N-partite W state, and therefore exhibit true $N$-fold entanglement. Furthermore, we show that for N=3, the correlations cannot be reproduced by a hybrid local-nonlocal hidden-variable model. For N >= 4 the issue remains open.
Bell Nonlocality as a Covariance Obstruction in Locally Covariant Quantum Field Theory
本文揭示了局部协变量子场论中贝尔非局域性与协变性的根本矛盾，证明了在保持相对论因果性的同时无法嵌入经典因果框架的不可能性。
The hierarchy of nonlocality and entanglement in multipartite systems is one of the fundamental problems in quantum physics. We study this topic in three-qubit systems considering the entanglement classification of stochastic local operations and classical communication (SLOCC). The equivalence under SLOCC divides threequbit states into separable, biseparable, W, and Greenberger-Horne-Zeilinger (GHZ) classes. The W and GHZ are two subclasses of genuine tripartite entanglement.We adopt the family of GHZ-symmetric states as a research subject, which share the symmetries of the GHZ state and have…
A dual-region ytterbium tweezer apparatus with an in-vacuum nanofiber cavity
该研究提出一种双区域镊子系统，通过移动黏胶输运原子至真空内纳米光纤腔附近，实现单原子装载，寿命达9.5秒，验证了架构的可行性。
We have recently (Heras et al. in Eur. Phys. J. Plus 136:847, 2021) argued that classical electrodynamics can predict nonlocal effects by showing an example of a topological and nonlocal electromagnetic angular momentum. In this paper we discuss the dual of this angular momentum which is also topological and nonlocal. We then unify both angular momenta by means of the electromagnetic angular momentum arising in the configuration formed by a dyon encircling an infinitely-long dual solenoid enclosing uniform electric and magnetic fluxes and show that this electromagnetic angular momentum is topo…
Quantum fluctuations of the vacuum are both a surprising and fundamental phenomenon of nature. Understood as virtual photons flitting in and out of existence, they still have a very real impact, \emph{e.g.}, in the Casimir effects and the lifetimes of atoms. Engineering vacuum fluctuations is therefore becoming increasingly important to emerging technologies. Here, we shape vacuum fluctuations using a "mirror", creating regions in space where they are suppressed. As we then effectively move an artificial atom in and out of these regions, measuring the atomic lifetime tells us the strength of t…
Hierarchy of quantum correlations in qubit-qutrit axially symmetric states
研究揭示了双极子-三极子系统中量子相关性的层次结构，发现贝尔非局域性最脆弱，而MIN和UIN更稳健，适用于实际条件下的量子性检测。
Recently, it has been shown that the massless quantum vacuum state contains entanglement between timelike separated regions of spacetime, in addition to the entanglement between the spacelike separated regions usually considered. Here, we show that timelike entanglement can be extracted from the Minkowski vacuum and converted into ordinary entanglement between two inertial, two-state detectors at the same spatial location -- one coupled to the field in the past and the other coupled to the field in the future. The procedure used here demonstrates a clear time correlation as a requirement for e…
Recently, there have been a number of works investigating the entanglement properties of distinct noncomplementary parts of discrete and continuous Bosonic systems in ground and thermal states. The Fermionic case, however, has yet to be expressly addressed. In this paper we investigate the entanglement between a pair of far-apart regions of the 3+1 dimensional massless Dirac vacuum via a previously introduced distillation protocol [B. Reznik et al., Phys. Rev. A 71, 042104 (2005)]. We show that entanglement persists over arbitrary distances, and that as a function of L/R, where L is the distan…
We employ an approach wherein vacuum entanglement is directly probed in a controlled manner. The approach consists of having a pair of initially nonentangled detectors locally interact with the field for a finite duration, such that the two detectors remain causally disconnected, and then analyzing the resulting detector mixed state. It is demonstrated that the correlations between arbitrarily far-apart regions of the vacuum of a relativistic free scalar field cannot be reproduced by a local hidden-variable model, and that as a function of the distance L between the regions, the entanglement d…
Signatures of the black hole quantum atmosphere in nonlocal correlations
本研究采用测量诱导非局域性度量探究黑洞附近的量子关联，发现其呈现量子大气特征，关联下降位置与大气辐射峰值重合，为验证霍金辐射起源于量子大气的观点提供新途径。
Various aspects of nonlocality of a quantum wave are discussed. In particular, the question of the possibility of extracting information about the relative phase in a quantum wave is analyzed. It is argued that there is a profound difference in the nonlocal properties of the quantum wave between fermion and boson particles. The phase of the boson quantum state can be found from correlations between results of measurements in separate regions. These correlations are identical to the Einstein-Podolsky-Rosen (EPR) correlations between two entangled systems. An ensemble of results of measurements …
We argue that the phenomenon of vacuum birefringence in strong inhomogeneous electromagnetic fields can be most efficiently analyzed in terms of a vacuum emission process. In this contribution, we exemplarily stick to the case of vacuum birefringence in a stationary perpendicularly directed, purely magnetic background field extending over a finite spatial extent. Similar field configurations are realized in the BMV and PVLAS experiments. We demonstrate that we can reproduce the conventional constant field result. Our focus is on effects which arise when the probe photons originate in the field…
We study the relations of the positive frequency mode functions of Dirac field in 4-dimensional Minkowski spacetime covered with Rindler and Kasner coordinates, and describe the explicit form of the Minkowski vacuum state with the quantum states in Kasner and Rindler regions, and analytically continue the solutions. As a result, we obtain the correspondence of the positive frequency mode functions in Kasner region and Rindler region in a unified manner which derives vacuum entanglement.
Quantum metasurfaces as probes of vacuum particle content
利用量子镜探测真空粒子内容，通过亚波长原子阵列实现对真空边界条件变化的高灵敏度测量。
Vacuum energy in quantum field theory, being the sum of zero-point energies of all field modes, is formally infinite but yet, after regularization or renormalization, can give rise to finite observable effects. One way of understanding how these effects arise is to compute the vacuum energy in an idealized system such as a large cavity divided into disjoint regions by pistons. In this paper, this type of calculation is carried out for situations where the potential affecting a field is not the same in all regions of the cavity. It is shown that the observable parts of the vacuum energy in such…
Positive frequency Wightman function and vacuum expectation values of the energy-momentum tensor are computed for a massive scalar field with general curvature coupling parameter and satisfying Robin boundary condition on a uniformly accelerated infinite plate. The both regions of the right Rindler wedge, (i) on the right (RR region) and (ii) on the left (RL region) of the plate are investigated. For the case (ii) the electromagnetic field is considered as well. The mode summation method is used with combination of a variant of the generalized Abel-Plana formula. This allows to present the exp…
Separate regions in space are generally entangled, even in the vacuum state. It is known that this entanglement can be swapped to separated Unruh-DeWitt detectors, i.e., that the vacuum can serve as a source of entanglement. Here, we demonstrate that, in the presence of curvature, the amount of entanglement that Unruh-DeWitt detectors can extract from the vacuum can be increased.
Vacuum expectation values of the field square and the energy-momentum tensor for the electromagnetic field are investigated for the geometry of a wedge with a coaxal cylindrical boundary. All boundaries are assumed to be perfectly conducting and both regions inside and outside the shell are considered. By using the generalized Abel-Plana formula, the vacuum expectation values are presented in the form of the sum of two terms. The first one corresponds to the geometry of the wedge without the cylindrical shell and the second term is induced by the presence of the shell. The vacuum energy densit…
We explore the entanglement of the vacuum of a relativistic field by letting a pair of causally disconnected probes interact with the field. We find that, even when the probes are initially non-entangled, they can wind up to a final entangled state. This shows that entanglement persists between disconnected regions in the vacuum. However the probe entanglement, unlike correlations, vanishes once the regions become sufficiently separated. The relation between entropy, correlations and entanglement is discussed.
Fermionic Casimir densities for a uniformly accelerating mirror in the Fulling-Rindler vacuum
研究均匀加速镜在(D+1)维平直时空中的Fulling-Rindler真空对费米子场的局部特性，分析边界诱导贡献及真空期望值，对比Minkowski真空行为。
In this paper we consider the question of the degree to which negative and positive energy are intertwined. We examine in more detail a previously studied quantum state of the massless minimally coupled scalar field, which we call a ``Helfer state''. This is a state in which the energy density can be made arbitrarily negative over an arbitrarily large region of space, but only at one instant in time. In the Helfer state, the negative energy density is accompanied by rapidly time-varying energy fluxes. It is the latter feature which allows the quantum inequalities, bounds which restrict the mag…
The geometric entanglement entropy of a quantum field in the vacuum state is known to be divergent and, when regularized, to scale as the area of the boundary of the region. Here we introduce an operational definition of the entropy of the vacuum restricted to a region: we consider a subalgebra of observables that has support in the region and a finite resolution. We then define the entropy of a state restricted to this subalgebra. For Gaussian states, such as the vacuum of a free scalar field, we discuss how this entropy can be computed. In particular we show that for a spherical region we re…
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