arXiv subjects
Publications and source records attributed to Hans-Juergen Stoeckmann.
The Bloch equations, which describe spin precession and relaxation in external magnetic fields, can be generalized to include the evolution of polarization tensors of various ranks in arbitrary multipole fields. The derivation of these generalized Bloch equations can be considerably simplified by using a particular bra-ket notation for irreducible tensors.
In the paper we analyze the "singular statistics" of pseudointegrable Seba billiards and show that taking into account growing number of resonances one observes the transition from "semi-Poissonian"-like statistics to Poissonian. This observation is in agreement with an argument that a classical particle does not feel a point perturbation. However, our findings contradict results reported earlier (P. Seba, Phys. Rev. Lett. 64, 1855 (1990)).
Following a recent work by Robnik and Romanovski (J.Phys.A: Math.Gen. {\bf 39} (2006) L35, Open Syst. & Infor. Dyn. {\bf 13} (2006) 197-222) we derive the explicit formula for the universal distribution function of the final energies in a time-dependent 1D harmonic oscillator, whose functional form does not depend on the details of the frequency $ω(t)$, and is closely related to the conservation of the adiabatic invariant. The normalized distribution function is $P(x) = π^{-1} (2μ^2 - x^2)^{-{1/2}}$, where $x=E_1- \bar{E_1}$, $E_1$ is the final energy, $\bar{E_1}$ is its average value, and $μ^2$ is the variance of $E_1$. $\bar{E_1}$ and $μ^2$ can be calculated exactly using the WKB approach to all orders.
In a previous contribution (H.J. Stoeckmann, J. Phys. A35, 5165 (2002)), the density of states was calculated for a billiard with randomly distributed delta-like scatterers, doubly averaged over the positions of the impurities and the billiard shape. This result is now extended to the k-point correlation function. Using supersymmetric methods, we show that the correlations in the bulk are always identical to those of the Gaussian Unitary Ensemble (GUE) of random matrices. In passing from the band centre to the tail states, The density of states is depleted considerably and the two-point correlation function shows a gradual change from the GUE behaviour to that found for completely uncorrelated eigenvalues. This can be viewed as similar to a mobility edge.
Using the one-to-one correspondence between the Poynting vector in a microwave billiard and the probability current density in the corresponding quantum system probability densities and currents were studied in a microwave billiard with a ferrite insert as well as in an open billiard. Distribution functions were obtained for probability densities, currents and vorticities. In addition the vortex pair correlation function could be extracted. For all studied quantities a complete agreement with the predictions from the random-superposition-of-plane-waves approach was obtained.
In this work we study the eigenstates and the energy spectra of a generic billiard system with the use of microwave resonators. This is possible due to the exact correspondence between the Schroedinger equation and the electric field equations of the lowest modes in thin microwave resonators. We obtain a good agreement between the numerical (exact) and experimental eigenstates, while the short range experimental spectral statistics show the expected Brody-like behaviour in this energy range, as opposed to the Berry-Robnik picture which is valid only in the semiclassical region of sufficiently small effective Planck's constant.