Aharonov-Bohm effect: a standalone construct

Yakir Aharonov and David Bohm's 1959 paper Significance of Electromagnetic Potentials in the Quantum Theory named the effect in which a charged particle, such as an electron, acquires a measurable shift in its quantum phase (the internal clock-like angle that governs how its wave interferes with itself) while travelling through a region where the electric and magnetic fields are zero but the electromagnetic potentials are not, a result W. Ehrenberg and R. E. Siday had already derived a decade earlier in 1949. The finding was striking because classical physics holds that only the fields, not the potentials, can act on a particle, so a phase shift arising in a field-free region shows that the potentials carry physical consequences in quantum mechanics. R. G. Chambers reported the first experimental sign of the shift in 1960 using an electron interferometer and a fine magnetic whisker, and Akira Tonomura and colleagues confirmed it in 1986 with the magnetic flux fully enclosed and shielded from the electron path. As a landmark the effect is measured by the displacement of the fringes in an electron interference pattern and scales with the enclosed magnetic flux, and it established gauge potentials, together with the topology of the space a particle can reach, as observable elements of quantum theory rather than mere mathematical bookkeeping.[1][2][3][4]

Unit

A quantum-mechanical phenomenon: a phase shift in a charged particle's wavefunction, measured in radians and proportional to the enclosed magnetic flux

Recovery means

Not applicable

Measured by

Detected as a displacement of the fringes in an electron interference pattern, with the shift proportional to the magnetic flux enclosed between the two electron paths