INSPIRE: Testing Bell's Inequality with Astrophysical Observations

INSPIRE项目由数学与物理科学局（MPS）物理部（PHY）原子、分子和光学物理实验项目、物理与物理科学局（PHY /MPS）原子、分子和光学物理理论项目、粒子天体物理学和宇宙学理论项目、MPS天文学（AST）部门的星系外天文学与宇宙学项目和科学、技术、科学、技术、科学、技术、科学、技术、科学和技术、科学、技术和技术、科学、技术和技术部门共同资助。社会、行为和经济科学司（SBE）社会经济科学司（SES）、教育和人力资源司（EHR）研究生教育司（DGE）、综合活动办公室和国际科学与工程办公室。近一个世纪以来，物理学家利用量子力学来理解物理世界的许多特性，从原子和分子的行为到控制亚原子粒子的核力。理论预测与实验观察相吻合，精确到无可挑剔。然而，从概念上讲，该理论包含了一些非常奇怪的特征。其中最奇怪的是“量子纠缠”。根据量子力学，以特殊方式制备的粒子可以保持联系，即使它们彼此之间的距离是任意远的——阿尔伯特·爱因斯坦将这种特性称为“幽灵般的远距离作用”。如今，纠缠是许多尖端技术的核心，包括量子加密和量子计算。然而，迄今为止，每一个关于量子纠缠的实验测试都存在各种漏洞：不同于量子理论的其他解释可能会解释粒子行为中的远距离相关性。在这个项目中，主要研究人员的目标是解决这些漏洞中最顽固、研究最少的漏洞，即“设置独立性漏洞”。为了防止粒子和测量仪器之间出现任何意想不到的协调——这种协调可能会模仿量子力学的预测——选择要测量的粒子的哪些特性将通过对我们宇宙中一些最古老的光的实时观测来决定：这种光是由离地球很远的天体发出的，它们彼此之间也很遥远，以至于在它们发出今天在地球上观测到的光之前，两个天体都无法接收到对方的任何信号。因此，新的一系列实验将在一个全新的尺度上测试纠缠。如果像预期的那样，结果与量子力学的预测相匹配，那么任何替代方案都将被排除或受到严格限制，而量子加密等新技术将被置于最强大的基础上。另一方面，如果实验发现了与预测不同的新奇之处，那可能会指向全新的物理学。这个项目也有一个非正式的教育组成部分，将通过麻省理工学院博物馆的展览和项目进行；随着实验的实时发展，这些将把公众与实验联系起来，并将得到评估和广泛传播。贝尔不等式的实验测试有几个漏洞，这些漏洞使单个粒子同时具有非交换变量的尖锐值的可能性（无论多么微小）成为可能。这种行为将与量子力学相悖，并将使量子加密协议面临新的漏洞。最微妙的漏洞被称为“设置独立性”。在任何纠缠测试中，必须在实验装置的每一边选择探测器设置，选择测量，例如，一个粒子沿着x轴、y轴或某个中间角度的自旋。通常的假设是，在纠缠粒子和测量仪器的共同因果过去中，没有第三方影响探测器设置的联合概率分布。然而，即使是探测器设置和纠缠粒子之间的微小协调，也可能模拟量子力学的预测。在这一系列的实验中，主要研究人员的目标是通过对遥远的天文源（如类星体）的实时观测来解决设置独立的漏洞。类星体在发出今天在地球上观测到的光时，是相互隔离的，也与地球的世界线隔绝。因此，实验各元素之间的任何非量子力学协调都将被推回到数十亿年前，在某些情况下，可以追溯到大爆炸本身，这比目前的限制条件提高了20个数量级。

This INSPIRE project is jointly funded by the Atomic, Molecular, and Optical Physics--Experiment Program in the Physics (PHY) Division in the Directorate for Mathematics and Physical Sciences (MPS), and the Atomic, Molecular, and Optical Physics--Theory Program in PHY/MPS, and the Particle Astrophysics and Cosmology--Theory Program in PHY/MPS, and the Extragalactic Astronomy & Cosmology Program in the Astronomy (AST) Division of MPS, and the Science, Technology, and Society Program in the Division of Social and Economic Sciences (SES) in the Directorate for Social, Behavioral, and Economic Sciences (SBE), and the Division of Graduate Education (DGE) in the Directorate for Education & Human Resources (EHR),and the Office of Integrative Activities and the Office of International Science and Engineering. For nearly a century, physicists have used quantum mechanics to understand many properties of the physical world, from the behavior of atoms and molecules to the nuclear forces that govern sub-atomic particles. Predictions from the theory have matched experimental observations to impeccable accuracy. Conceptually, however, the theory includes some strikingly strange features. Among the most curious is known as "quantum entanglement." According to quantum mechanics, particles that have been prepared in a special way can retain a connection, even after they have moved arbitrarily far apart from each other--a property which Albert Einstein dubbed "spooky actions at a distance." Nowadays entanglement is at the heart of many cutting-edge technologies, including quantum encryption and quantum computing. Yet every experimental test of quantum entanglement to date has been subject to various loopholes: alternative explanations, different than quantum theory, that might account for the long-distance correlations in the particles' behavior. In this project, the principal investigators aim to address the most stubborn, and least studied, of these loopholes, known as the "setting independence loophole." To shield against any unintended coordination between the particles and the measurement apparatus--coordination that could mimic the predictions of quantum mechanics--the selection of which properties of the particles to be measured will be determined by real-time observation of some of the oldest light in our universe: light that was emitted from astronomical objects so far away from Earth and from each other that neither object would have been able to receive any signals from each other prior to the moment they emitted the light that is observed on Earth today. The new series of experiments will thus test entanglement on an entirely new scale. If, as expected, the results match the predictions from quantum mechanics, then any alternatives will be ruled out or severely constrained, and new technologies such as quantum encryption will be placed on the strongest possible footing. If, on the other hand, the experiment finds novel departures from predictions, that could point toward profoundly new physics. This project also has an informal education component that will take place through exhibits and programs at the MIT Museum; these will connect the public to the experiment as it evolves in real time, and will be evaluated and widely disseminated. Experimental tests of Bell's inequality have been subject to several loopholes which hold out the possibility, however slim, that individual particles could possess simultaneously sharp values for noncommuting variables. Such behavior would be at odds with quantum mechanics, and would subject quantum-encryption protocols to new vulnerabilities. The most subtle loophole is known as "setting independence." In any test of entanglement, one must select detector settings on each side of the experimental apparatus, choosing to measure, for example, a particle's spin along the x-axis, the y-axis, or some intermediate angle. The usual assumption is that no third party, acting in the shared causal past of the entangled particles and the measurement apparatus, has affected the joint probability distribution for detector settings. Yet even a tiny coordination among detector settings and the entangled particles could mimic the predictions of quantum mechanics. In this series of experiments, the principal investigators aim to address the setting-independence loophole using real-time observations of distant astronomical sources, such as quasars--sources that were causally isolated from each other and from the worldline of the Earth at the time they emitted the light that is observed on Earth today. Any non-quantum-mechanical coordination among elements of the experiment would thereby be pushed back billions of years, in some scenarios back to the big bang itself, an improvement of 20 orders of magnitude over current constraints.