Tunable Einstein-Bohr Recoiling-Slit Gedankenexperiment at the Quantum Limit

作者：Yu-Chen Zhang, Haowen Cheng, Zhao-Qiu Zengxu, Zhan Wu, Rui Lin, Yu-Cheng Duan, Jun Rui, Ming-Cheng Chen, Chao‐Yang Lu, Jian-Wei Pan · 发表于：Physical Review Letters · 年份：2025 · DOI：10.1103/93zb-lws3 · 被引用次数：9 · 研究领域：Quantum Information and Cryptography、Cold Atom Physics and Bose-Einstein Condensates、Quantum Mechanics and Applications

In 1927, during the fifth Solvay Conference, Einstein and Bohr described a double-slit interferometer with a "movable slit" that can detect the momentum recoil of one photon. Their debate centered on this Gedankenexperiment has provided profound insights into the central concepts of quantum mechanics. Despite many efforts to reproduce this conceptual experiment, a linear-optical version with a movable, quantum-limited slit and tunable momentum width remained challenging. Here, we report a realization of the Einstein-Bohr interferometer using a single atom in an optical tweezer, which is cooled to the motional ground state in three dimensions such that its momentum uncertainty is comparable to that of a single photon. We design an interferometric configuration where the single atom serves as an ultralight, quantum-limit beam splitter that is momentum entangled with the input photon. By varying the trap depth of the optical tweezer, we dynamically tune the atom's intrinsic momentum uncertainty, thus enabling the observation of a gradual shift in the visibility of single-photon interference. The interferometer also allows us to distinguish the classical noise caused by atom heating from the quantum-limited noise due to the momentum transfer, illustrating a quantum-to-classical transition.