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arXiv:quant-ph/9906063 · Physical Review A

Interrelations between the neutron’s magnetic interactions and the magnetic Aharonov-Bohm effect

E. Comay

Published Sep 11, 2000• 3 citations
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Abstract

It is proven that the phase shift of a polarized neutron interacting with a spatially uniform time-dependent magnetic field demonstrates the same physical principles as the magnetic Aharonov-Bohm effect. The crucial role of inert objects is explained, thereby proving the quantum-mechanical nature of the effect. It is also proven that the nonsimply connectedness of the force-free region is not a profound property of the system, and that it cannot be regarded as a sufficient condition for a nonzero phase shift.

DOI
10.1103/physreva.62.042102

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It is proven that the phase shift of a polarized neutron interacting with a spatially uniform time-dependent magnetic field demonstrates the same physical principles as the magnetic Aharonov-Bohm effect. The crucial role of inert objects is explained, thereby proving the quantum-mechanical nature of the effect. It is also proven that the nonsimply connectedness of the force-free region is not a profound property of the system, and that it cannot be regarded as a sufficient condition for a nonzero phase shift.
In the scalar Aharonov-Bohm effect, a charged particle (electron) interacts with the scalar electrostatic potential U in the field-free (i.e., force-free) region inside an electrostatic cylinder (Faraday cage). Using a perfect single-crystal neutron interferometer we have performed a ``dual'' scalar Aharonov-Bohm experiment by subjecting polarized thermal neutrons to a pulsed magnetic field. The pulsed magnetic field was spatially uniform, precluding any force on the neutrons. Aligning the direction of the pulsed magnetic field to the neutron magnetic moment also rules out any classical torque acting to change the neutron polarization. The observed phase shift is purely quantum mechanical in origin. A detailed description of the experiment, performed at the University of Missouri Research Reactor, and its interpretation is given in this paper.
A phase shift for de Broglie waves due to the action of a scalar potential in an otherwise field-free (i.e., force-free) region of space is known as the scalar Aharonov-Bohm (AB) effect. Unlike the more familiar AB effect due to the magnetic vector potential, the scalar effect has hitherto remained unverified due, presumably, to technical difficulties in electron interferometry. We have performed an analogous interferometric experiment with thermal neutrons subject to pulsed magnetic fields. The observations were carried out at the University of Missouri Research Reactor using a skew-symmetric perfect-silicon-crystal neutron interferometer. The expected phase shifts have been observed to a high degree of accuracy. A detailed description of the experiment and its interpretation is given in this paper.
The Aharonov-Bohm (AB) effect highlights the fundamental role of electromagnetic potentials in quantum mechanics, manifesting as a phase shift for a charged particle in field-free regions. While well-established for static magnetic fluxes, the effect's behavior under time-varying fluxes remains an open and debated question. Employing the WKB method, we derive the AB phase shift for a time-dependent magnetic vector potential, demonstrating that for circular paths in the quasistatic regime, it is proportional to the time-averaged enclosed magnetic flux, ΔφAB=1T∫0TeΦ(t) dtΔφ_{\rm AB} = \frac{1}{T} \int_0^T e Φ(t) \, dtΔφAB​=T1​∫0T​eΦ(t)dt, with the total phase shift, including kinetic contributions, equaling eΦ(0)e Φ(0)eΦ(0). For non-circular paths, the phase shift depends on both the flux history and path geometry, revealing the effect's hybrid nature involving gauge potentials and induced electric fields. We verify the consistency of our gauge choice with Maxwell's equations and discuss the implications for local versus nonlocal interpretations of the AB effect. We also generalize the results to scenarios with nonzero external magnetic fields, where the enclosed flux is through the actual electron paths, and for circular paths of radius RRR, the AB phase shift is also proportional to the time average of the enclosed flux Φenc(R,t)Φ_{\rm enc}(R,t)Φenc​(R,t), with the total phase shift depending only on the initial enclosed flux eΦenc(R,0)e Φ_{\rm enc}(R,0)eΦenc​(R,0); for general non-circular paths, the external magnetic field affects trajectories and phase accumulation through the Lorentz force, leading to additional path dependence. These findings clarify the role of gauge-dependent potentials and induced fields in the generalized AB effect, offering new theoretical insights and potential applications in quantum technologies.
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The Aharonov-Bohm effect is a physical phenomenon in which the quantum state of a charged particle acquires a phase shift that is directly proportional to the magnetic flux, ΦΦΦ, due to a (classical) magnetic field, B{\mathbf B}B, which is confined in a spatial region from which the magnetic field cannot escape. Even though the charged particle is not allowed to interact with the magnetic field, it accumulates a phase shift that affects the interference pattern produced. Not surprisingly, this apparent nonlocality is puzzling and counter intuitive. In this work, we provide an explanation that explains the physics underlying this apparent nonlocality. We find that the role of the confined magnetic field is to impart a puncture in the configuration space, R2\mathbb{R}^2R2, of the charge. Therefore, the quantum state corresponding to the charged quantum particle acquires the phase shift due to its response to the modified topology of the configuration space, R2−{0}\mathbb{R}^2-\{0\}R2−{0}, corresponding to the charge.