Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2410.10664 · Physical Review Letters

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

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

Published Oct 17, 2025• 10 citations
arXivHTMLPDF

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.

DOI
10.1103/93zb-lws3

Related papers

Objective Recoil and Complementarity in the Single-Atom Einstein–Bohr Experiment: A Physical–Observation Dual-Axis Formulation

Xianwei Meng

Nearly a century after the 1927 Solvay exchange, the Einstein–Bohr recoiling-slit experiment has been realized with a single optically trapped 87Rb atom. The atom is light enough for one scattered photon to leave a resolvable motional record, and sufficiently controllable for the overlap of the two opposite recoil states to be tuned across the quantum regime. The resulting visibility curve is commonly read as an experimental confirmation of Bohr. That reading is correct, but incomplete: the same experiment also makes visible the objective recoil carrier on which Einstein’s argument rested. We develop a physical–observation dual-axis formulation in which the photon path x ∈ X and the atomic motional state s ∈ S enter as irreducible state coordinates of the observed fact r = F(x,s). The joint photon atom state then gives a complex cross-axis coherence kernel γS = ⟨s−|s+⟩. Its modulus is the photon visibility, its phase transports the fringe origin, and the distinguishability of the same two recoil records supplies the available path information. For a Gaussian motional ground state the construction yields V = exp(−2η2), with η = hk /(2∆p), reproducing the dependence tested in the experiment. We also prove that, whenever controlled atomic states generate different complex kernels at fixed photon preparation, no photon-only response map can represent the complete phase-resolved family of observations. Standard quantum mechanics satisfies this requirement by retaining the composite state; the dual-axis formulation makes its observational structure explicit. The resulting synthesis is precise: Einstein was right about the reality and physical location of the recoil record, while Bohr was right about the bound governing its coexistence with interference. Neither the necessity of a classical apparatus cut nor the completeness of quantum single-event dynamics follows from the experiment. Phase-sensitive and closed-loop extensions are proposed to probe the complex cross-axis response beyond visibility alone.

•Sep 10, 2026•0 citations

Squeezed-slit Bohr-Einstein Interferometer

Hao-Wen Cheng, Xu-Zhao-Qiu Zeng, Yu-Chen Zhang +9 more

The Einstein-Bohr recoiling-slit gedankenexperiment, a cornerstone of quantum complementarity, has long been constrained by the zero-point fluctuations of the atomic slit -- the spatial Standard Quantum Limit (SQL). Here we transcend this fundamental boundary through active quantum state engineering of a single-atom slit. By implementing a non-adiabatic quench-evolve-quench protocol, we prepare the atomic motion in a squeezed state, dynamically redistributing phase-space uncertainty to suppress which-path information and restore high-visibility interference beyond the static vacuum limit. We report an intrinsic visibility of $0.938_{-0.008}^{+0.004}$, violating the SQL ($0.819$) by over 10 standard deviations, corresponding to $7.6(2)$ dB of effective squeezing. Our work reveals Kerr-induced non-Gaussian dynamics and reinterprets the traditional interferometer as a powerful tool for continuous-variable Wigner tomography, bridging the gap between quantum foundations and advanced metrology.

quant-pharXiv:2605.28038•May 28, 2026•0 citations

Physical Distortion of Equivalent Slit Model Using Single Atomic Scattering

Jiaqing Yan

Published in 2025, the recoiling-slit quantum interference experiment employs optically trapped single rubidium atoms to scatter photons. It claims to physically realize Einstein’s thought experiment of a movable physical slit and supports the principle of quantum complementarity based on experimental observations. Within the framework of the Original Light Theory, this paper strictly distinguishes the microscopic motion of individual photons and the statistical characteristics of photon ensembles. From the perspectives of acting environment, spatial scale and microscopic coupling mechanism, we demonstrate that the single rubidium atom scattering system only shares approximate mathematical appearances with the traditional double-slit system with physical wall thickness, while their physical essences are entirely different. This experiment artificially eliminates core physical conditions in real double-slit systems, including photon oscillation, slit channels and continuous momentum coupling between photons and slit walls, which constitutes typical conceptual substitution. Fundamentally, it is merely a recoil scattering experiment between single photons and isolated rubidium atoms, and cannot be equated with physical double-slit interference experiments. Once the inherent oscillation of photons and the mechanism of continuous interaction between photons and thick slit walls are incorporated, there is no basis for the equivalence of the two sets of models. Asserting model equivalence while ignoring photon oscillation and slit-wall coupling effects is nothing but self-deception. Its experimental conclusions are highly misleading. They cannot be extended to interpret real thick-wall double-slit interference and cannot serve as reliable experimental evidence for the validity of the principle of complementarity. Previous theoretical analyses built on physical slit models remain fully valid. Divergences originate from the replacement of experimental physical models rather than defects in the original physical mechanism analysis.

•Jul 25, 2026•0 citations

A New Interpretation of the Recoiling-Slit Quantum Interference Experiment

Jiaqing Yan

In December 2025, Pan Jianwei’s research team reproduced the Einstein-Bohr recoiling-slit thought experiment proposed in 1927 at the quantum limit. They observed that the interference fringe contrast changes continuously with the momentum of the slit. Mainstream physical theories currently regard this phenomenon as critical evidence for the quantum complementarity principle. Based on the Light Primitive Theory, this paper points out that all relevant theoretical models established since the century-long debate at the Solvay Conference contain two fundamental idealized simplifications: first, physical slits are abstracted as two-dimensional geometric holes with zero thickness; second, the inherent continuous spatial oscillation of photons is ignored. Photons are not point-like particles moving along fixed straight lines. Their persistent oscillation enables continuous momentum coupling between photons and the photon self-locked matter forming the slit walls throughout the whole passage through the physically thick slit channel. The inverse correlation between path detectability and interference fringe visibility observed in the experiment can be self-consistently explained by continuous photon-slit wall interaction, without abstract hypotheses such as wave-particle complementarity or quantum superposition. This paper supplements the objective physical conditions missing from traditional models and provides a brand-new interpretative framework for quantum interference phenomena at the underlying mechanism level.

•Jul 25, 2026•0 citations

Einstein–Bohr recoiling double-slit gedanken experiment performed at the molecular level

X.-J. Liu, Quan Miao, Faris Gel’mukhanov +6 more

Double-slit experiments illustrate proof for wave–particle complementarity. The essence of Einstein–Bohr's debate about wave–particle duality was whether the momentum transfer between a particle and a recoiling slit could mark the path, thus destroying the interference. We realized this recoiling double-slit gedanken experiment by resonant X-ray photoemission from molecular oxygen for geometries near equilibrium (coupled slits) and in a dissociative state far away from equilibrium (decoupled slits). Interference is observed in the former case, while the electron momentum transfer quenches the interference in the latter case.

Journal of Physics Conference Series•Sep 7, 2015•1 citation

Complementarity and the Nature of Uncertainty Relations in Einstein–Bohr Recoiling Slit Experiment

Shogo Tanimura

A model of the Einstein–Bohr recoiling slit experiment is formulated in a fully quantum theoretical setting. In this model, the state and dynamics of a movable wall that has two slits in it, as well as the state of a particle incoming to the two slits, are described by quantum mechanics. Using this model, we analyzed complementarity between exhibiting an interference pattern and distinguishing the particle path. Comparing the Kennard–Robertson type and the Ozawa-type uncertainty relations, we conclude that the uncertainty relation involved in the double-slit experiment is not the Ozawa-type uncertainty relation but the Kennard-type uncertainty relation of the position and the momentum of the double-slit wall. A possible experiment to test the complementarity relation is suggested. It is also argued that various phenomena which occur at the interface of a quantum system and a classical system, including distinguishability, interference, decoherence, quantum eraser, and weak value, can be understood as aspects of entanglement. Quanta 2015; 4: 1–9.

arXiv:quant-ph/0703118•Quanta•Jul 15, 2015•3 citations
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.
Nearly a century after the 1927 Solvay exchange, the Einstein–Bohr recoiling-slit experiment has been realized with a single optically trapped 87Rb atom. The atom is light enough for one scattered photon to leave a resolvable motional record, and sufficiently controllable for the overlap of the two opposite recoil states to be tuned across the quantum regime. The resulting visibility curve is commonly read as an experimental confirmation of Bohr. That reading is correct, but incomplete: the same experiment also makes visible the objective recoil carrier on which Einstein’s argument rested. We develop a physical–observation dual-axis formulation in which the photon path x ∈ X and the atomic motional state s ∈ S enter as irreducible state coordinates of the observed fact r = F(x,s). The joint photon atom state then gives a complex cross-axis coherence kernel γS = ⟨s−|s+⟩. Its modulus is the photon visibility, its phase transports the fringe origin, and the distinguishability of the same two recoil records supplies the available path information. For a Gaussian motional ground state the construction yields V = exp(−2η2), with η = hk /(2∆p), reproducing the dependence tested in the experiment. We also prove that, whenever controlled atomic states generate different complex kernels at fixed photon preparation, no photon-only response map can represent the complete phase-resolved family of observations. Standard quantum mechanics satisfies this requirement by retaining the composite state; the dual-axis formulation makes its observational structure explicit. The resulting synthesis is precise: Einstein was right about the reality and physical location of the recoil record, while Bohr was right about the bound governing its coexistence with interference. Neither the necessity of a classical apparatus cut nor the completeness of quantum single-event dynamics follows from the experiment. Phase-sensitive and closed-loop extensions are proposed to probe the complex cross-axis response beyond visibility alone.
The Einstein-Bohr recoiling-slit gedankenexperiment, a cornerstone of quantum complementarity, has long been constrained by the zero-point fluctuations of the atomic slit -- the spatial Standard Quantum Limit (SQL). Here we transcend this fundamental boundary through active quantum state engineering of a single-atom slit. By implementing a non-adiabatic quench-evolve-quench protocol, we prepare the atomic motion in a squeezed state, dynamically redistributing phase-space uncertainty to suppress which-path information and restore high-visibility interference beyond the static vacuum limit. We report an intrinsic visibility of 0.938−0.008+0.0040.938_{-0.008}^{+0.004}0.938−0.008+0.004​, violating the SQL (0.8190.8190.819) by over 10 standard deviations, corresponding to 7.6(2)7.6(2)7.6(2) dB of effective squeezing. Our work reveals Kerr-induced non-Gaussian dynamics and reinterprets the traditional interferometer as a powerful tool for continuous-variable Wigner tomography, bridging the gap between quantum foundations and advanced metrology.
Published in 2025, the recoiling-slit quantum interference experiment employs optically trapped single rubidium atoms to scatter photons. It claims to physically realize Einstein’s thought experiment of a movable physical slit and supports the principle of quantum complementarity based on experimental observations. Within the framework of the Original Light Theory, this paper strictly distinguishes the microscopic motion of individual photons and the statistical characteristics of photon ensembles. From the perspectives of acting environment, spatial scale and microscopic coupling mechanism, we demonstrate that the single rubidium atom scattering system only shares approximate mathematical appearances with the traditional double-slit system with physical wall thickness, while their physical essences are entirely different. This experiment artificially eliminates core physical conditions in real double-slit systems, including photon oscillation, slit channels and continuous momentum coupling between photons and slit walls, which constitutes typical conceptual substitution. Fundamentally, it is merely a recoil scattering experiment between single photons and isolated rubidium atoms, and cannot be equated with physical double-slit interference experiments. Once the inherent oscillation of photons and the mechanism of continuous interaction between photons and thick slit walls are incorporated, there is no basis for the equivalence of the two sets of models. Asserting model equivalence while ignoring photon oscillation and slit-wall coupling effects is nothing but self-deception. Its experimental conclusions are highly misleading. They cannot be extended to interpret real thick-wall double-slit interference and cannot serve as reliable experimental evidence for the validity of the principle of complementarity. Previous theoretical analyses built on physical slit models remain fully valid. Divergences originate from the replacement of experimental physical models rather than defects in the original physical mechanism analysis.
In December 2025, Pan Jianwei’s research team reproduced the Einstein-Bohr recoiling-slit thought experiment proposed in 1927 at the quantum limit. They observed that the interference fringe contrast changes continuously with the momentum of the slit. Mainstream physical theories currently regard this phenomenon as critical evidence for the quantum complementarity principle. Based on the Light Primitive Theory, this paper points out that all relevant theoretical models established since the century-long debate at the Solvay Conference contain two fundamental idealized simplifications: first, physical slits are abstracted as two-dimensional geometric holes with zero thickness; second, the inherent continuous spatial oscillation of photons is ignored. Photons are not point-like particles moving along fixed straight lines. Their persistent oscillation enables continuous momentum coupling between photons and the photon self-locked matter forming the slit walls throughout the whole passage through the physically thick slit channel. The inverse correlation between path detectability and interference fringe visibility observed in the experiment can be self-consistently explained by continuous photon-slit wall interaction, without abstract hypotheses such as wave-particle complementarity or quantum superposition. This paper supplements the objective physical conditions missing from traditional models and provides a brand-new interpretative framework for quantum interference phenomena at the underlying mechanism level.
Double-slit experiments illustrate proof for wave–particle complementarity. The essence of Einstein–Bohr's debate about wave–particle duality was whether the momentum transfer between a particle and a recoiling slit could mark the path, thus destroying the interference. We realized this recoiling double-slit gedanken experiment by resonant X-ray photoemission from molecular oxygen for geometries near equilibrium (coupled slits) and in a dissociative state far away from equilibrium (decoupled slits). Interference is observed in the former case, while the electron momentum transfer quenches the interference in the latter case.
A model of the Einstein–Bohr recoiling slit experiment is formulated in a fully quantum theoretical setting. In this model, the state and dynamics of a movable wall that has two slits in it, as well as the state of a particle incoming to the two slits, are described by quantum mechanics. Using this model, we analyzed complementarity between exhibiting an interference pattern and distinguishing the particle path. Comparing the Kennard–Robertson type and the Ozawa-type uncertainty relations, we conclude that the uncertainty relation involved in the double-slit experiment is not the Ozawa-type uncertainty relation but the Kennard-type uncertainty relation of the position and the momentum of the double-slit wall. A possible experiment to test the complementarity relation is suggested. It is also argued that various phenomena which occur at the interface of a quantum system and a classical system, including distinguishability, interference, decoherence, quantum eraser, and weak value, can be understood as aspects of entanglement. Quanta 2015; 4: 1–9.