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We consider scattering of a three-dimensional particle on a finite family of potentials. For some parameter values the scattering wavefunctions exhibit nodal lines in the form of closed loops, which may touch but do not entangle. The corresponding probability current forms vortical singularities around these lines; if the scattered particle is charged, this gives rise to magnetic flux loops in the vicinity of the nodal lines. The conclusions extend to scattering on hard obstacles or smooth potentials.

We discuss properties of the two-dimensional Landau Hamiltonian perturbed by a family of identical <i></i> potentials arranged equidistantly along a closed loop. It is demonstrated that for the loop size exceeding the effective size of the point obstacles and the cyclotronic radius such a system exhibits persistent currents at the bottom of the spectrum. We also show that the effect is sensitive to a small disorder.

Motivation: quantum kinematics of decays, with and without repeated measurements Zeno dynamics: existence, form of the generator Anti-Zeno effect: what is it and under which conditions it can occur? Solvable model: a caricature description of a system of a quantum wire and dots Comparison: relations between the stable and Zeno dynamics in this and other models

In this paper, we prove that the existence of absolutely continuous spectrum of the Kirchhoff Laplacian on a radial metric tree graph together with a finite complexity of the geometry of the tree implies that the tree is in fact eventually periodic. This complements the results by Breuer and Frank in (Rev Math Phys 21(7):929945, 2009) in the discrete case as well as for sparse trees in the metric case.