arXiv subjects

H. Thomas

Publications and source records attributed to H. Thomas.

21 records · Page 2Linked to original sources

arXiv1998

1D Toy Model For Trapping Neutral Particles

We study, both classically and quantum-mechanically, the problem of a neutral particle with spin, moving in one-dimension in an inhomogeneous magnetic field. This problem serves for us as a toy model to study the trapping of neutral particles. We identify K, the ratio between the precessional frequency of the particle and its vibration frequency, as the relevant parameter of the problem. Classicaly, we find that when the magnetic moment is antiparallel to the direction of the magnetic field, the particle is trapped provided that K<0.5. We also find that viscous friction, be it translational or precessional, destabilizes the system. Quantum-mechanically, we study the problem of spin half particle in the same field. Treating K as a small parameter for the perturbation from the adiabatic Hamiltonian, we find the lifetime of the particle in its trapped ground-state.

physics.class-ph↗

arXiv1998

On the Spinning Motion of the Hovering Magnetic Top

In this paper we analyze the spinning motion of the hovering magnetic top. We have observed that its motion looks different from that of a classical top. A classical top rotates about its own axis which precesses around a vertical fixed external axis. The hovering magnetic top, on the other hand, has its axis slightly tilted and moves rigidly as a whole about the vertical axis. We call this motion synchronous, because in a stroboscopic experiment we see that a point at the rim of the top moves synchronously with the top axis. We show that the synchronous motion may be attributed to a small deviation of the magnetic moment from the symmetry axis of the top. We calculate the minimum angular velocity required for stability in terms of the moments of inertia and magnetic field and show that it is different from that of a classical top. We also give experimental results that were taken with a top whose moment of inertia can be changed. These results show very good agreement with our calculations.

physics.class-ph↗

arXiv1997

Front Propagation in Evanescent Media

We investigate the time evolution of waves in evanescent media generated by a source within this medium and observed at some distance away from the location of the source. The aim is to find a velocity which describes a causal process and is thus, for a medium with relativistic dispersion, limited by the velocity of light. The wave function consists of a broad frequency forerunner generated by the onset of the source, and of a monochromatic front which carries the oscillation frequency of the source. For a medium with Schrödinger-like dispersion the monochromatic front propagates with a velocity which is in agreement with the traversal time, and in the relativistic case the velocity of the fronts is limited by the velocity of light. For sources with a sharp onset, the forerunners are not attenuated and in magnitude far exceed the monochromatic front. In contrast, for sources which are frequency-band limited, the forerunners are also attenuated and become comparable to the monochromatic front: like in the propagating case, there exists a time at which a broad frequency forerunner is augmented by a monochromatic wave.

quant-ph↗