We use an extended version of electrodynamics, which admits the existence of
magnetic charges and currents, to discuss how different models for electric and
magnetic dipoles do or do not carry hidden momentum under the influence of
external electromagnetic fields. Based on that, we discuss how the models
adopted for the electric and magnetic dipoles from the particles that compose a
material medium influence the expression for the electromagnetic part of the
light momentum in the medium. We show that Abraham expression is compatible
with electric dipoles formed by electric charges and magnetic dipoles formed by
magnetic charges, while Minkowski expression is compatible with electric
dipoles formed by magnetic currents and magnetic dipoles formed by electric
currents. The expression $\varepsilon_0\mb{E}\times\mb{B}$, on the other hand,
is shown to be compatible with electric dipoles formed by electric charges and
magnetic dipoles formed by electric currents, which are much more natural
models. So this expression has an interesting interpretation in the
Abraham-Minkowski debate about the momentum of light in a medium: It is the
expression compatible with the nonexistence of magnetic charges. We also
provide a simple justification of why Abraham and Minkowski momenta can be
associated with the kinetic and canonical momentum of light, respectively.Comment: 5 pages. v2: Minor changes on the tex
By using perturbation theory, we show that a hydrogen atom with magnetic moment due to the orbital angular momentum of the electron has "hidden momentum" in the presence of an external electric field. This means that the atomic electronic cloud has a nonzero linear momentum in its center-of-mass rest frame due to a relativistic effect. This is completely analogous to the hidden momentum that a classical current loop has in the presence of an external electric field. We discuss that this effect is essential for the validity of the Lorentz force law in quantum systems. We also connect our results to the long-standing Abraham-Minkowski debate about the momentum of light in material media.
We explore quantum properties of a which-way detector using three versions of an idealized two slit arrangements. Firstly we derive complementarity relations for the detector; secondly we show how the "experiment" may be altered in such a way that using single position measurement on the screen we can obtain quantum erasure. Finally we show how to construct a superposition of "wave" and "particle" components.
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