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Momentum Transfer to a Free Floating Double Slit:
A Realization of Einstein´s Thought Experiment

If we shrink the double slit arrangement to microscopic dimensions the quantum properties of the slits impact on the double slit interference pattern. This effect was first debated by Einstein and Bohr as they tried to understand the newly developed ideas of quantum physics. Einstein argued, in one of his famous thought experiments, that it should be possible to determine the scattered particle’s path after it has interfered by measuring its momentum transfer to the slit arrangement.

We measured the diffraction pattern of Helium atoms which were scattered from HD molecules. The two nuclei of the molecule constitute the double slit. The orientation of the molecule at the time of the scattering was inferred from the emission directions of the molecular fragments post scattering. An interference pattern of the scattered Helium is observed because the uncertainty relation prevents a determination of the scattered particle´s pathway, as was claimed by Bohr. However, the interference pattern is bent. To explain this experimental observation we have developed a quantum mechanical model in which the interference of the scattered particle is completely described by its influence on the quantum properties of the slit arrangement. Furthermore, we show that a classical treatment of the slits can still be employed to describe the data, but only if a non classical description of the interaction is assumed.

Figure 1: Realization of a Thought Experiment from the Einstein-Bohr Debates: Helium is scattered from an HD molecule and the recoil effect measured with a precision at the quantum limit.

Press release on the subject (only in german):

Article in „Physik Journal“ describing this work (in german)
Doppelspalt in HD, Physik Journal 12 (2013) Nr. 11


Momentum Transfer to a Free Floating Double Slit: Realization of a Thought Experiment from the Einstein-Bohr Debates
L. Ph. H. Schmidt, J. Lower, T. Jahnke, S. Schößler, M. S. Schöffler, A. Menssen, C. Lévêque, N. Sisourat, R. Taïeb, H. Schmidt-Böcking, and R. Dörner
DOI: 10.1103/PhysRevLett.111.103201
Phys. Rev. Lett. 111, 103201 (2013)