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

Nature Photonics volume 9, pages 120125 (2015) | Download Citation


Double-slit experiments illustrate the quintessential proof for wave–particle complementarity. If information is missing about which slit the particle has traversed, the particle, behaving as a wave, passes simultaneously through both slits. This wave-like behaviour and corresponding interference is absent if ‘which-slit’ information exists. 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. To measure the recoil of a slit, the slits should move independently. We showcase a materialization of 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 owing to Doppler labelling of the counter-propagating atomic slits, in full agreement with Bohr's complementarity.

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Experiments were performed at the PLEIADES beamline at SOLEIL synchrotron, France (proposal no. 99110013). The authors thank N. Kosugi for sharing knowledge of the oxygen molecule, D. Serban and P. Morin for stimulating discussions about the physical interpretation, E. Robert for technical assistance and the SOLEIL staff for the smooth running of the facility. This work is supported by a public grant from the ‘Laboratoire d'Excellence Physics Atoms Light Matter’ (LabEx PALM) overseen by the French National Research Agency (ANR) as part of the ‘Investissements d'Avenir’ programme (reference no. ANR-10-LABX-0039). The research leading to these results has also received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 252781 and the European Cooperation in Science and Technology (COST) action CM1204–XUV/X-ray light and fast ions for ultrafast chemistry (XLIC), from Triangle de la Physique under contract no. 2007-010T, from the Japan Society for the Promotion of Science (JSPS) and from the Swedish Research Council (VR) under grants nos 621-2012-3675 (F.G.) and 621-2012-3347 (H.Å.).

Author information


  1. Synchrotron SOLEIL, l'Orme des Merisiers, Saint-Aubin, BP 48, 91192 Gif-sur-Yvette Cedex, France

    • Xiao-Jing Liu
    • , Faris Gel'mukhanov
    • , Minna Patanen
    • , Oksana Travnikova
    • , Christophe Nicolas
    •  & Catalin Miron
  2. Theoretical Chemistry and Biology, School of Biotechnology, Royal Institute of Technology, S-106 91 Stockholm, Sweden

    • Quan Miao
    • , Faris Gel'mukhanov
    •  & Hans Ågren
  3. College of Electronics, Communication and Physics, Shandong University of Science and Technology, Qingdao, 266590 Shandong, China

    • Quan Miao
  4. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan

    • Kiyoshi Ueda
  5. Extreme Light Infrastructure – Nuclear Physics (ELI-NP), ‘Horia Hulubei’ National Institute for Physics and Nuclear Engineering, 30 Reactorului Street, RO-077125 Măgurele, Jud. Ilfov, Romania

    • Catalin Miron


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C.M. suggested and designed the experiment. X.L. upgraded the experimental set-up and carried out the data analysis. X.L., M.P., C.N. and O.T. participated in data acquisition. F.G. and C.M. proposed the data interpretation. H.Å. contributed to the data interpretation. F.G. designed the theory. Q.M. performed the theoretical simulations. F.G., H.Å. and C.M. wrote the paper. X.L., Q.M. and C.N. participated in the production of figures. All authors discussed the results and commented on the manuscript.

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The authors declare no competing financial interests.

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Correspondence to Catalin Miron.

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