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Universality of local weak interactions and its application to interferometer alignment
Shimshon Bar-Ad [1] , Demitry Farfurnik [1], , Nimrod Benshalom [1], , Jonathan Efroni [1], , Lev Vaidman [1] , Jan Dziewior [2], , Lukas Knips [2], , Katharina Senkalla [2], , Jasmin Meinecke [2], , Harald Weinfurter [2]
[1] Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 69978, Israel
[2] Max-Planck-Institute for Quantum Optics, 85748 Garching, Germany, and Department of Physics, Ludwig-Maximilians-University, 80797 Munchen, Germany
The modification of the effect of interactions of a particle as a function of its preselected and postselected states is analyzed theoretically and experimentally, and the universality of this modification in the case of local interactions of a spatially preselected and postselected particle is demonstrated. It allows us to define an operational approach for the characterization of the presence of a quantum particle in a particular place, namely the way it modifies the effect of local weak interactions. The experimental implementation, which entangles the transverse degrees of freedom of photons with their path in a Mach-Zehnder interferometer, also allows us to demonstrate a novel and efficient method of interferometer alignment, where the trajectory of the postselected beam on a single quadrant detector, throughout a single phase scan, yields all the misalignment parameters.