The Entangling Power of Spacetime

量子物理学和引力是现代物理学的两个基本支柱，尽管理论物理学界做出了大量努力来统一它们，但它们仍然不相容。这个提议是关于使用一种叫做纠缠收获的新方法来提高我们对它们关系的理解。它将量子纠缠现象（也许是量子物理学中最奇怪的方面）与黑洞（引力物理学中最令人困惑的物体）结合在一起。在过去的十年里，人们已经清楚地认识到，时空既可以纠缠量子比特，也可以摧毁它们所携带的信息。量子纠缠、探测器响应、量子场和时空结构之间存在着微妙的关系。本提案的目标是通过为其描述提供坚实的理论基础来研究这种关系，并获得可以通过实验测试（或至少模拟）的预测。量子比特可以被视为具有高（激发）或低（接地）内能的理想探测器。纠缠收获利用了两个原本独立的量子位在暴露于量子真空时会纠缠在一起的特性。因此，量子位提取（收获）这种真空纠缠，其数量取决于它们的分离、相对运动，最重要的是，取决于它们附近的空间和时间结构。这里引入引力：它使空间和时间弯曲，因此探测器提取的纠缠提供了引力如何影响量子纠缠的信息。这个提议的重点是黑洞如何影响两个量子位可以收获和保存的纠缠。黑洞比任何其他物体更能弯曲时空，将任何冒险靠近其边缘的物体困住。它们吸收一切而不释放任何物质，显然违反了热力学第二定律（即无序或熵总是增加）。量子物理学暗示黑洞会辐射（辐射的粒子与内部伙伴纠缠在一起），增加混乱，恢复第二定律。但奇怪的是，随着黑洞的蒸发，它的辐射会“与虚无纠缠在一起”，这在正常的量子物理学中是不可能的。这就是黑洞信息悖论：恢复第二定律的量子物理学最终预测了一个矛盾的情况。纠缠收集将用于观察实际的量子物体（量子位）在靠近黑洞时、黑洞形成时以及其中一个（或两个）落入黑洞时是如何纠缠的。通过量化纠缠如何依赖于这些不同设置中的量子位分离、能量和运动，我们将了解有关时空量子结构的新信息。该研究项目的影响将是关于黑洞纠缠特性的重要新知识，对信息悖论产生新的见解，并推动引力与量子物理的调和。

Quantum physics and gravity, the two foundational pillars of modern physics, remain incompatible despite substantive efforts by the theoretical physics community to unite them. This proposal is about advancing our understanding of their relationship using a novel approach called entanglement harvesting. It brings together the phenomenon of quantum entanglement, perhaps the strangest aspect of quantum physics, with black holes, the most perplexing objects in gravitational physics. Over the past decade it has become clear that spacetime has the capacity to both entangle qubits and to destroy the information they carry. A subtle relationship exists between quantum entanglement, detector responses, quantum fields, and the structure of spacetime. The goal of this proposal is to investigate this relationship by providing both a firm theoretical foundation for its description, and to obtain predictions that can be tested (or at least simulated) by experiment. Qubits can be regarded as idealized detectors that can have high (excited) or low (ground) internal energy. Entanglement harvesting exploits the property that 2 otherwise independent qubits will become entangled upon exposure to the quantum vacuum. The qubits therefore extract (harvest) this vacuum entanglement, the amount depending on their separation, relative motion, and - most importantly - on the structure of space and time in their vicinity. Here gravity is introduced: it curves space and time, so that the entanglement the detectors extract provides information as to how gravity influences quantum entanglement. This proposal focuses on how black holes impact the entanglement that 2 qubits can harvest and preserve. Black holes curve spacetime more than any other objects, trapping anything venturing too close to their edge. Absorbing everything and emitting nothing, they apparently violate the 2nd law of thermodynamics (that disorder, or entropy, always increases). Quantum physics implies black holes radiate (the radiated particles being entangled with inside partners), increasing disorder and restoring the 2nd law. But strangely, as the hole evaporates away, its radiation becomes `entangled with nothing', a situation impossible in normal quantum physics. This is the black hole information paradox: the quantum physics restoring the 2nd law ultimately predicts a contradictory situation. Entanglement harvesting will be used to see how actual quantum objects (the qubits) become entangled when they are near black holes, when black holes form, and when one (or both) falls into a black hole. By quantifying how entanglement depends on qubit separation, energy, and motion in these various settings, we will learn new information about the quantum structure of spacetime. The impact of this research program will be important new knowledge about the entangling properties of black holes, yield new insight into the information paradox, and advance the reconciliation of gravity with quantum physics.