The Aharonov—Bohm effect (for short: AB effect) is, quite generally, a non-local effect in which a physical object travels along a closed loop through a gauge field-free region and thereby undergoes a physical change. As such, the AB effect can be described as a holonomy. Its paradigmatic realization became widely known after Aharonov and Bohm's 1959 paper — with forerunners by Weiss  and Ehrenberg and Siday . Aharonov and Bohm  consider the following scenario: A split electron beam passes around a solenoid in which a magnetic field is confined. The region outside the solenoid is field-free, but nevertheless a shift in the interference pattern on a screen behind the solenoid can be observed upon alteration of the magnetic field. The schematic experimental setting can be grasped from the following figure:
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