Tunable Einstein-Bohr recoiling-slit gedankenexperiment at the quantum limit

TL;DR

This paper demonstrates a quantum version of the Einstein-Bohr recoiling-slit experiment using a single atom in an optical tweezer, showing tunable quantum interference and a transition to classical noise.

Contribution

It presents a faithful realization of the Einstein-Bohr interferometer with a single atom, enabling tunable quantum interference at the quantum limit.

Findings

Observation of interferometric visibility reduction with shallower traps

Identification of classical noise sources such as atom heating and precession

Demonstration of a quantum-to-classical transition in the experiment

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. Here, we report a faithful realization of the Einstein-Bohr interferometer using a single atom in an optical tweezer, cooled to the motional ground state in three dimensions. The single atom has an intrinsic momentum uncertainty comparable to a single photon, which serves as a movable slit obeying the minimum Heisenberg uncertainty principle. The atom's momentum wavefunction is dynamically tunable by the tweezer laser power, which enables observation of an interferometric visibility reduction at a shallower trap, demonstrating the quantum nature of this interferometer. We further identify classical noise due to atom heating and precession, illustrating a quantum-to-classical transition.