INSPIRE: Testing Bell's Inequality with Astrophysical Observations

这项INSPIRE计划是由数学与物理科学局(MPS)物理部(PHY)的原子、分子和光学物理--实验计划、PHY/MPS的原子、分子和光学物理--理论计划、PHY/MPS的粒子天体物理和宇宙学--理论计划、以及河外天文学与AMP共同资助的。MPS天文学(AST)部的宇宙学计划，社会、行为和经济科学局(SBE)的社会和经济科学部(SES)的科学、技术和社会计划，教育与人力资源局(EHR)的研究生教育部(DGE)，以及综合活动办公室和国际科学和工程办公室。近一个世纪以来，物理学家一直使用量子力学来理解物理世界的许多属性，从原子和分子的行为到支配亚原子粒子的核力。该理论的预测与实验观测结果相吻合，准确度无可挑剔。然而，从概念上讲，这一理论包含了一些惊人的奇怪特征。其中最令人好奇的就是所谓的“量子纠缠”。根据量子力学，以一种特殊方式制备的粒子可以保持联系，即使它们彼此之间移动了任意的距离--阿尔伯特·爱因斯坦将这种特性称为“远距离的幽灵行为”。如今，纠缠是包括量子加密和量子计算在内的许多尖端技术的核心。然而，到目前为止，对量子纠缠的每一次实验测试都受到了各种漏洞的影响：与量子理论不同的另一种解释，可能会解释粒子行为中的长距离关联。在这个项目中，主要调查人员的目标是堵住这些漏洞中最顽固、最少被研究的漏洞，即所谓的“设置独立漏洞”。为了屏蔽粒子和测量仪器之间的任何意外协调--这种协调可以模仿量子力学的预测--选择要测量的粒子的哪些属性将取决于对我们宇宙中一些最古老的光的实时观察：这些光是从远离地球和彼此的天文物体发出的，以至于在发出今天在地球上观察到的光之前，这两个物体都无法接收到彼此的任何信号。因此，新的一系列实验将在一个全新的尺度上测试纠缠。如果如预期的那样，结果与量子力学的预测相符，那么任何替代方案都将被排除或受到严格限制，量子加密等新技术将被置于尽可能强大的基础上。另一方面，如果实验发现与预测有新的偏离，那就可能指向深刻的新物理学。该项目还有一个非正式的教育部分，将通过麻省理工学院博物馆的展品和项目进行；这些将在实验实时发展的过程中将公众与其联系起来，并将得到评估和广泛传播。贝尔不等式的实验测试一直存在几个漏洞，这些漏洞表明，尽管可能性很小，但单个粒子可能同时具有非对易变量的尖锐值。这种行为将与量子力学相抵触，并将使量子加密协议面临新的漏洞。最微妙的漏洞就是所谓的“设置独立性”。在任何纠缠测试中，必须选择实验设备两边的探测器设置，例如，选择测量粒子沿x轴、y轴或某个中间角的自旋。通常的假设是，在纠缠粒子和测量设备的共同因果过去中，没有第三方影响探测器设置的联合概率分布。然而，即使探测器设置和纠缠粒子之间的微小协调也可以模拟量子力学的预测。在这一系列实验中，主要研究人员旨在通过对遥远的天文光源进行实时观测来解决与环境无关的漏洞，例如类星体--这些光源在发射今天在地球上观察到的光时，由于原因而彼此隔离，并与地球的世界线隔绝。因此，实验元素之间的任何非量子力学协调都将被推迟数十亿年，在某些情况下，将回到大爆炸本身，比目前的限制提高了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.