Atomic Hong-Ou-Mandel experiment

摘要

Two-particle interference is a fundamental feature of quantum mechanics, and is even less intuitive than wave-particle duality for a single particle. In this duality, classical concepts-wave or particle-are still referred to, and interference happens in ordinary space-time. On the other hand, two-particle interference takes place in a mathematical space that has no classical counterpart. Entanglement lies at the heart of this interference, as it does in the fundamental tests of quantum mechanics involving the violation of Bell's inequalities. The Hong, Ou and Mandel experiment is a conceptually simpler situation, in which the interference between two-photon amplitudes also leads to behaviour impossible to describe using a simple classical model. Here we report the realization of the Hong, Ou and Mandel experiment using atoms instead of photons. We create a source that emits pairs of atoms, and cause one atom of each pair to enter one of the two input channels of a beam-splitter, and the other atom to enter the other input channel. When the atoms are spatially overlapped so that the two inputs are indistinguishable, the atoms always emerge together in one of the output channels. This result opens the way to testing Bell's inequalities involving mechanical observables of massive particles, such as momentum, using methods inspired by quantum optics, and to testing theories of the quantum-to-classical transition. Our work also demonstrates a new way to benchmark non-classical atom sources that may be of interest for quantum information processing and quantum simulation.%"Hong-Ou-Mandel效应"（在该效应中，进入一个50:50分束器的两个不可分辨的光子导致检测器的"符合率"下降）反映了量子力学理论的基本特征，在经典力学中没有同样现象。它是很多量子信息和量子光学实验的基础。在这项研究中，Marc Cheneau及同事在关于"原子对"之生成的以前进展的基础上，通过氦-4原子而不是光子实现了"Hong-Ou-Mandel"实验。由于原子与光子相比是大质量粒子，所以该实验为用大质量粒子的可观察量进行基本量子物理实验(如Bell tests)提供了可能性。从长远来讲，这将有助于关于量子力学中物质和引力之效应的研究工作，尤其是与"量子—经典"转变相关的研究工作。