伟大的争论灿烂的前景——量子信息的由来及展望

量子力学完备性的争论导致了贝尔不等式的建立和漫长的高精技术的检验，结果不仅肯定了量子力学的完备性，而且揭示了它的“非定域性特征”和其独有的“纠缠态”的资源性内涵，从而引领了量子信息理论和应用研究的热潮，展现了全新信息技术的光辉灿烂的前景。     

具有Dzialoshinski-Moriya相互作用的XXZ自旋链所形成热态的贝尔不等式违背

研究了Dzialoshinski-Moriya（DM）相互作用对由XXZ自旋链所形成热态的贝尔不等式违背的影响.结果表明DM相互作用和具有较大正值的各向异性参数可以增强贝尔不等式的违背并能够提高贝尔不等式违背的临界温度.通过贝尔不等式违背和热纠缠的对比,发现热纠缠的临界温度高于贝尔不等式违背的临界温度,这表明一些量子纠缠态不违背贝尔不等式.     

关于量子力学完备性的跨世纪之争

概述了关于量子力学完备性的跨世纪之争,包括爱因斯坦-玻尔论战、量子力学的几率诠释、“波包收缩”、“EPR论证”(在许多文章和书中被错误地称作“EPR佯谬”)、“隐变量理论”和“贝尔不等式”．建议采用一种时间、空间的新定义,以克服“波包收缩”解释的因难．     

围绕Aspect实验的学术争论

介绍了围绕Aspect实验发生的争论，指出Aspect实验与玻尔同爱因斯 坦两位科学巨人之争密切相关，阐述了玻坶思想实验与贝尔不等式的重要意义。     

有界域上一维双极量子力学模型解的经典极限（英文）

考虑一维双极等熵量子力学模型.首先,对方程进行一些变形,利用Poincarés不等式及函数收敛和弱收敛的一些性质,得到了稳态解的经典极限,即当普朗克常量ε趋于0时,量子力学模型方程的稳态解趋于经典力学模型方程的稳态解.然后,利用非稳态解已有的一些结论和Sobolev不等式,Schwartz不等式,Gronwall不等式及一些能量估计,得到了非稳态解的经典极限,即量子力学模型方程的光滑解趋于经典力学模型方程的光滑解.     

量子力学解释的经验主义视角——对Muynck的一个文本解读

通过对Muynck的量子力学的经验主义解释文本的解读,区分爱因斯坦和玻尔关于量子力学的完备性之争中"广义上的完备"和"狭义上的完备"的差异,以及他们对于量子力学描述物理实在所持有的"客观性"和"情境性"的不同理解,同时说明Muynck所倡导的量子力学的新的经验主义解释是对"哥本哈根解释"的修正与发展,它强调理论需要解释而不是非解释,不同于范.夫拉森的严格经验主义。这种新的经验主义解释有助于我们理解量子力学的特征。     

实在性、定域性和见尔不等式的若干讨论

本文介绍和讨论了实在性和定域性观念以及其数学化的表述——Bell不等式中的若干问题,指出某些与Bell不等式相联系的实验存在严重的缺陷.对实在性观念和量子力学的分歧重新给予了评论。     

狭义相对论研究中的若干问题

量子力学(QM)在本质上具有非经典性、微观性和非局域性,故量子力学与狭义相对论(SR)在根本上不具有一致性。EPR论文集中代表了爱因斯坦对量子力学的不满和捍卫狭义相对论自然观的意图。虽然狭义相对论不允许超光速状态,但量子力学的非局域性表示出现超光速是可能的。实际上,超光速问题是狭义相对论与量子力学有尖锐矛盾的证明。对已有超光速实验作分类整理后指出,不少实验很象是一种量子行为,而这些实验是对狭义相对论和量子力学理论研究的激励。最后指出,对光子静质量虽已做过许多研究,仍有一些问题有待解决。     

关于量子力学理论的解释

本文讨论量子力学理论的解释,认为波粒二象性并非互斥互补,而是可以在同一实验中同时出现的;测量中所测之量之所以有个不确定范围,不是来自仪器的不可控制的干扰,而是波粒二象性所致;微观粒子的运动规律目前之所以只能作出统计性的解释,并非因果律不适用,而是当前我们的知识尚不够完备。最后介绍一些有关量子力学理论解释的研究动向。     

联合概率与贝尔不等式

本文试图证明，贝尔不等式的破坏，并未否定定域性原理和决定论。它只是再一次证明“联合概率”这一概念不完全适用于微观物理学。     

定域隐变量理论的实验检验

<正> 一、历史上两种观点的争论量子力学的形式体系是完美的,它经受了半个多世纪的各种严格的实验检验,但是关于量子力学理论基础的解释,无论物理上还是哲学上都存在重大的原则分岐。假若把量子力学的形式体系彻底地贯彻到对现实物理世界的认识中去,那么势必导致与经典物理概念和传统哲学观念格格不入的新概念和新观点     

Experimental violation of a Bell's inequality with efficient detection

Local realism is the idea that objects have definite properties whether or not they are measured, and that measurements of these properties are not affected by events taking place sufficiently far away. Einstein, Podolsky and Rosen used these reasonable assumptions to conclude that quantum mechanics is incomplete. Starting in 1965, Bell and others constructed mathematical inequalities whereby experimental tests could distinguish between quantum mechanics and local realistic theories. Many experiments have since been done that are consistent with quantum mechanics and inconsistent with local realism. But these conclusions remain the subject of considerable interest and debate, and experiments are still being refined to overcome 'loopholes' that might allow a local realistic interpretation. Here we have measured correlations in the classical properties of massive entangled particles (9Be+ ions): these correlations violate a form of Bell's inequality. Our measured value of the appropriate Bell's 'signal' is 2.25 +/- 0.03, whereas a value of 2 is the maximum allowed by local realistic theories of nature. In contrast to previous measurements with massive particles, this violation of Bell's inequality was obtained by use of a complete set of measurements. Moreover, the high detection efficiency of our apparatus eliminates the so-called 'detection' loophole.     

Violation of a Bell-like inequality in single-neutron interferometry

Non-local correlations between spatially separated systems have been extensively discussed in the context of the Einstein, Podolsky and Rosen (EPR) paradox and Bell's inequalities. Many proposals and experiments designed to test hidden variable theories and the violation of Bell's inequalities have been reported; usually, these involve correlated photons, although recently an experiment was performed with (9)Be(+) ions. Nevertheless, it is of considerable interest to show that such correlations (arising from quantum mechanical entanglement) are not simply a peculiarity of photons. Here we measure correlations between two degrees of freedom (comprising spatial and spin components) of single neutrons; this removes the need for a source of entangled neutron pairs, which would present a considerable technical challenge. A Bell-like inequality is introduced to clarify the correlations that can arise between observables of otherwise independent degrees of freedom. We demonstrate the violation of this Bell-like inequality: our measured value is 2.051 +/- 0.019, clearly above the value of 2 predicted by classical hidden variable theories.     

Generation of three-qubit entangled states using superconducting phase qubits

Entanglement is one of the key resources required for quantum computation, so the experimental creation and measurement of entangled states is of crucial importance for various physical implementations of quantum computers. In superconducting devices, two-qubit entangled states have been demonstrated and used to show violations of Bell's inequality and to implement simple quantum algorithms. Unlike the two-qubit case, where all maximally entangled two-qubit states are equivalent up to local changes of basis, three qubits can be entangled in two fundamentally different ways. These are typified by the states |GHZ>= (|000+?|111>)/ sqrt [2] and |W>= (|001>?+?|010>?+?|100>)/ sqrt [3]. Here we demonstrate the operation of three coupled superconducting phase qubits and use them to create and measure |GHZ> and |W>states. The states are fully characterized using quantum state tomography and are shown to satisfy entanglement witnesses, confirming that they are indeed examples of three-qubit entanglement and are not separable into mixtures of two-qubit entanglement.     

Bell不等式及其局域性假设

文中首先证明Bell不等式成立的充足条件是几率的Kolmogorov模型.不等式破缺只说明对量子关联系统Kolmogorov模型失效.其次,Bell的局域性假设不能与 Einstein 的“分离性”条件等价,它隐含有苛刻的几率约束条件,最后指出了 Bell 不等式也不是完全地符合量子理论的预测.因此,量子理论基础问题的讨论,并没有由于 Bell 不等式的实验验证作出判决.     

Bell型空间非定域性研究现状与展望

尽管和经典理论一样,从非相对论量子力学到相对论量子场论的量子理论采用了定域描述的方法,但本质上,量子理论却是在定域描述外衣下的空间非定域理论.从著名的EPR佯谬发难,Bell不等式的提出,GHZ定理,Hardy定理到Cabello定理,长期以来围绕Bell-GHZ-Hardy-Cabello这条空间非定域性研究路线,涌现出大量的理论和实验工作,文献汗牛充栋.迄今实验结果总是支持量子理论,但远远没能揭示出量子理论空间非定域性的本质,也未能否定隐变量的存在.这种状况使这一热点问题仍然吸引着很多人的关注和思考.我们对这条研究路线作了全面而简要地总结,系统而明确地叙述了有关的思想、概念和定理,最后给出了对它的详细评论.     

Experimental entanglement distillation and 'hidden' non-locality

Entangled states are central to quantum information processing, including quantum teleportation, efficient quantum computation and quantum cryptography. In general, these applications work best with pure, maximally entangled quantum states. However, owing to dissipation and decoherence, practically available states are likely to be non-maximally entangled, partially mixed (that is, not pure), or both. To counter this problem, various schemes of entanglement distillation, state purification and concentration have been proposed. Here we demonstrate experimentally the distillation of maximally entangled states from non-maximally entangled inputs. Using partial polarizers, we perform a filtering process to maximize the entanglement of pure polarization-entangled photon pairs generated by spontaneous parametric down-conversion. We have also applied our methods to initial states that are partially mixed. After filtering, the distilled states demonstrate certain non-local correlations, as evidenced by their violation of a form of Bell's inequality. Because the initial states do not have this property, they can be said to possess 'hidden' non-locality.     

Weyl和Heisenberg不确定性不等式的新推广

利用一个辅助的定积分恒等式，我们对描述量子力学中确定性原理的著名的Ｗｅｙｌ及Ｈｅｉｓｅｎｂｅｒｇ不等式建立若干新的推广。     

原子分子体系的引力效应

寻找完整的量子引力理论是目前理论物理中的前沿热点问题之一,而黑洞热力学和量子干涉仪探测引力效应被认为是正在形成的量子引力理论的两个重要的"实验区".前者通过将量子概念引入到广义相对论来检验二者如何结合,特别是量子力学幺正性将在这两个理论的结合中经受严峻考验;而后者通过量子系统在引力场背景中的演化来试验引力对系统量子属性的影响,在这一方面广义相对论等效原理在微观粒子领域将接受越来越严格的实验检验.目前,原子分子物理实验中出现了类似黑洞辐射的现象,然而,这些现象出现的理论机制还不是非常明确,究竟能否用目前已有的理论解释,或者还是需要构建新的理论来解释也是不清楚的,但是无论如何,这些现象的出现为实验研究量子引力理论打开了一扇窗户.另一方面,人们已经使用量子系统测量一些弱引力效应,这不仅为研究引力对量子系统的影响提供了便利条件,也为研究二者结合提供了一个好的突破口.本综述将结合我们近几年的工作,围绕原子分子体系中的强引力和弱引力效应来介绍和讨论这些问题.     

Experimental non-classicality of an indivisible quantum system

In contrast to classical physics, quantum theory demands that not all properties can be simultaneously well defined; the Heisenberg uncertainty principle is a manifestation of this fact. Alternatives have been explored--notably theories relying on joint probability distributions or non-contextual hidden-variable models, in which the properties of a system are defined independently of their own measurement and any other measurements that are made. Various deep theoretical results imply that such theories are in conflict with quantum mechanics. Simpler cases demonstrating this conflict have been found and tested experimentally with pairs of quantum bits (qubits). Recently, an inequality satisfied by non-contextual hidden-variable models and violated by quantum mechanics for all states of two qubits was introduced and tested experimentally. A single three-state system (a qutrit) is the simplest system in which such a contradiction is possible; moreover, the contradiction cannot result from entanglement between subsystems, because such a three-state system is indivisible. Here we report an experiment with single photonic qutrits which provides evidence that no joint probability distribution describing the outcomes of all possible measurements--and, therefore, no non-contextual theory--can exist. Specifically, we observe a violation of the Bell-type inequality found by Klyachko, Can, Binicio?lu and Shumovsky. Our results illustrate a deep incompatibility between quantum mechanics and classical physics that cannot in any way result from entanglement.