自发参量下转换中的不可分Werner态

Gaussian entanglement witness and refined Werner-Wolf criterion for continuous variables

We use matched quantum entanglement witnesses to study the separable criteria of continuous variable states. The witness can be written as an identity operator minus a Gaussian operator. The optimization of the witness then is transformed to an eigenvalue problem of a Gaussian kernel integral equation. It follows a separable criterion not only for symmetric Gaussian quantum states, but also for non-Gaussian states prepared by photon adding to or/and subtracting from symmetric Gaussian states. Based on Fock space numeric calculation, we obtain an entanglement witness for more general two-mode s…

Local-hidden-state models for T-states using finite shared randomness

The study of local models using finite shared randomness originates from the consideration about the cost of classically simulating entanglement in composite quantum systems. We construct explicitly two families of local-hidden-state (LHS) models for T-states, by mapping the problem to the Werner state. The continuous decreasing of shared randomness along with entanglement, as the anisotropy increases, can be observed in the one from the most economical model for the Werner state. The construction of the one for separable states shows that the separable boundary of T-states can be generated fr…

具有正部分转置的纠缠连续变量Werner态的不存在性

Nonexistence of entangled continuous-variable Werner states with positive partial transpose

我们解决了一个关于纠缠连续变量（CV）Werner态存在性的公开问题。我们证明，没有这样的国家存在的所有PPT CV维尔纳状态是可分离的。可分离性如下观察到，这些CV维尔纳状态可以近似截断成一个有限维的产品状态的凸混合的状态。此外，产品状态的成分包括一个广义的非高斯测量，而令人惊讶的是，严格的上限量子不和谐比光子计数。这些结果揭示了只有负的部分转置纠缠的存在，并说明了更一般的非经典关联的复杂性，在这类典型的真正的非高斯量子态。

Werner态的量子纠缠相变

Quantum Entanglement Phase Transition in Werner State

为了解决量子态复杂性量化问题，提出了计算力学复杂性测度的一种扩展.通过一些简单的修改，该方法适用于qudits的任何$n-$部分状态。一个沃纳状态被认为是测试这种方法。结果表明，它经历了一个相变之间的纠缠和可分离的版本。另外，研究结果还表明了量子态复杂性鲁棒性的提高和纠缠之间的相互作用.最后，仅通过符号动力学统计分析，所提出的方法能够区分可分离和纠缠的动力学结构差异。

Geometric criterion for separability based on local measurement

A geometric understanding of entanglement is proposed based on local measurements. Taking recourse to the general structure of density matrices in the framework of Euclidean geometry, we first illustrate our approach for bipartite Werner states. It is demonstrated that separable states satisfy certain geometric constraints that entangled states do not. A separability criterion for multiparty Werner states of arbitrary dimension is derived. This approach can be used to determine separability across any bipartition of a general density matrix and leads naturally to a computable measure of entang…

噪声信道中纠缠量子态的可分性

Separability of entangled qutrits in noisy channels

我们提出了一个分析噪声原子通道涉及qutrits。我们选取一个V型三能级原子作为量子态。Gell-Mann矩阵和广义Bloch向量（8维）被用来描述quutrit密度算子。我们引入量子准分布的qutrits提供了一个简单的描述纠缠。通过对原子变量随时间演化的研究，我们发现了自发发射量子信道（SE信道）的Kraus表象。此外，我们考虑了两量子态的广义Werner态，并研究了在自发发射噪声存在下的可分离性条件。比较了自发发射对量子态和量子比特态的Werner态可分性的影响。

Teleportation via maximally and non-maximally entangled mixed states

We study the efficacy of two-qubit mixed entangled states as resources for quantum teleportation. We first consider two maximally entangled mixed states, viz., the Werner state\cite{werner}, and a class of states introduced by Munro {\it et al.} \cite{munro}. We show that the Werner state when used as teleportation channel, gives rise to better average teleportation fidelity compared to the latter class of states for any finite value of mixedness. We then introduce a non-maximally entangled mixed state obtained as a convex combination of a two-qubit entangled mixed state and a two-qubit separa…

Quantum Disentanglement Eraser: an optical implementation using three-photon spontaneous decay

The 'disentanglement eraser' or 'entanglement restorer' scheme allows retrieving entanglement by erasing the information about the formation of a classical (or separable) state. It suggests an analogy between the pairs of properties: entangled-separable and wave-particle, the latter as described in the 'quantum eraser'. The scheme illustrates the physical importance of information in quantum systems, and it is also useful as a building block for quantum computation. An optical setup for its simple implementation using three-photon decay in a centro-symmetrical crystal is proposed.

利用光的偏振和轨道角动量生成任意不可分离态

Generating arbitrary non-separable states with polarization and orbital angular momentum of light

提出一种利用偏振与OAM自由度生成任意光不可分离态的实验方法，并通过强度投影、偏振度和线性熵验证，为量子通信与传感提供可迁移方案。

非绝对可分性的资源理论

Resource Theory of Non-absolute Separability

该研究构建非绝对可分态的资源理论，提出两种非绝对可分性量化方法并验证其合理性，揭示纯态NAS含量的维度特性，建立该测度与纠缠量化子的关联，以Werner态验证结果。

不可分态的可分Schmidt模

Separable Schmidt modes of a non-separable state

在高维希尔伯特空间中，与波矢或频率等连续变量纠缠的双光子态是量子信息协议的一个强大资源。同时，存在单独寻址对应施密特模式的问题。我们提出了一种工程双光子光谱振幅的方法，以这样一种方式，它包含几个不重叠的施密特模式，其中每一个都可以被过滤lossslightly。该方法是基于自发参量下转换（SPDC）与梳状光谱的辐射泵浦。产生这种光谱的方法有很多种，这里我们考虑最简单的一种，即将泵浦光通过法布里-珀罗干涉仪。为了使双光子光谱振幅（TPSA）由非重叠的施密特模组成，晶体的色散依赖性、晶体的长度、法布里-珀罗自由光谱范围及其精细度应满足一定的条件。我们实验证明通过这些参数的TPSA的控制。我们还讨论了一种可能性，以实现类似的情况下，使用基于腔的SPDC。

通过零附加损耗光子多路复用启发协议的可分离态纠缠分发

Entanglement distribution through separable states via a zero-added-loss photon multiplexing inspired protocol

本文基于零附加损耗多路复用源，分析两种可分离态纠缠分发协议，考虑噪声影响，确定最优协议以最大化远距离纠缠产生。

在波导和环形谐振器中产生可分离光子三重态的策略

Strategies for generating separable photon triplets in waveguides and ring resonators

针对光子三重态光谱相关性问题，本文分析自发三阶参量下转换，并提出波导色散工程与谐振器泵浦工程两种可分离态生成策略。

耗散介质中的动态Casimir效应：何时终态不可分？

Dynamical Casimir Effect in dissipative media: When is the final state non-separable ?

我们研究的后果耗散均匀介质中的系统时，受到突然的变化，从而产生对相关的准粒子相反的动量。我们计算频谱的修改和相关性的修改。特别是，我们计算最终的一致性水平，并确定状态是不可分离的政权。为了分离耗散的作用，我们首先考虑色散介质，研究引起相干性的跳跃强度与降低相干性的温度之间的竞争，清楚地确定了受激发射和自发发射的贡献。然后，我们研究耗散如何修改这种竞争。

Characterizing Multipartite Non-Gaussian Entanglement for Three-Mode Spontaneous Parametric Down-Conversion Process

Very recently, strongly non-Gaussian states have been observed via a direct three-mode spontaneous parametric down-conversion in a superconducting cavity [Phys. Rev. X 10, 011011 (2020)]. The created multi-photon non-Gaussian correlations are attractive and useful for various quantum information tasks. However, how to detect and classify multipartite non-Gaussian entanglement has not yet been completely understood. Here, we present an experimentally practical method to characterize continuous-variable multipartite non-Gaussian entanglement, by introducing a class of nonlinear squeezing paramet…

反向自发参量下转换光源在锂铌酸盐绝缘体上的应用

Counter-propagating spontaneous parametric down-conversion source in lithium niobate on insulator

本研究提出了一种反向传播的集成光子对源，实现了高纯度和可调的光子源，为量子光子网络提供了可扩展的解决方案。