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

by Dr Magdalena Zych (SU)

Tuesday 3 Feb 2026, 15:00 → 16:00 Europe/Stockholm

AlbaNova A5:1041 - CoPS grupprum (AlbaNova Main Building)

authors: group of Jan-Wei Pan

abstract: 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

paper link: https://journals.aps.org/prl/abstract/10.1103/93zb-lws3