We study approximations of billiard systems by lattice graphs. It is demonstrated that under natural assumptions the graph wave functions approximate solutions of the Schrödinger equation with energy rescaled by the billiard dimension. As an example, we analyze a Sinai billiard with attached leads. The results illustrate emergence of global structures in large quantum graphs and offer interesting comparisons with patterns observed in complex networks of a different nature.
In this letter, the scattering state solutions of the Dirac equation for spin and pseudospin symmetries are obtained for the Hellmann potential. The normalized wave functions and scattering phase shifts are calculated for both spin and pseudospin symmetries. Scattering properties for Coulomb-like and Yukawa-like potentials are also studied as limiting cases.
We present the results of experimental studies of microwave irregular networks and a three-dimensional microwave rough cavity in the presence of absorption. Microwave networks are also analyzed numerically. Microwave networks simulate one-dimensional quantum graphs. The networks consist of coaxial cables connected by joints and attenuators to control absorption. Three-dimensional microwave rough cavities have no formal analog in quantum 3D systems. However, some statistical properties of their spectra such as the level spacing distribution confirms that they belong to the wave-chaotic systems. Absorption of the cavity was changed by using a foam microwave absorber.
Reflection and transmission measurements in microwave billiards with attached antennas allow the determination of all components of the scattering matrix including their phases. This is an extraordinary situation, since in usual scattering experiments in nuclear or atomic physics only reduced information such as the scattering cross-section can be obtained where the phase information is completely lost. This allows experimental tests of theoretical predictions of scattering theory inaccessible by any other method. As an example the distribution of reflection coefficients and of the line widths in a chaotic microwave billiard are discussed.
The recent paper by Hul et al. (Phys. Rev. Lett. 109, 040402 (2012)}, see Ref. [7]) addresses an important mathematical problem whether scattering properties of wave systems are uniquely connected to their shapes? The analysis of the isoscattering microwave networks presented in this paper indicates a negative answer to this question. In this paper the sensitivity of the spectral properties of the networks to boundary conditions is tested. We show that the choice of the proper boundary conditions is extremely important in the construction of the isoscattering networks.
In this paper, the scattering states of the spinless-Salpeter equation are investigated for Hulthén and hyperbolic-type potentials for any arbitrary l-state. Approximate analytical formulae of the wave functions and the scattering phase shifts are reported.
We present the results of numerical and experimental studies of the elastic enhancement factor W for microwave rough and rectangular cavities simulating two-dimensional chaotic and partially chaotic quantum billiards in the presence of moderate absorption. We show that for the frequency range ν=15.0-18.5 GHz, in which the coupling between antennas and the system is strong enough, the values of W for the microwave rough cavity lie below the predictions of random matrix theory and on average above the theoretical results of V. Sokolov and O. Zhirov, Phys. Rev. E 91, 052917 (2015). We also show that for the partially chaotic rectangular billiard the enhancement factor W calculated by applying the Potter-Rosenzweig model with κ=2.8±0.5 is close to the experimental one.
The autocorrelation function c(x) of level velocities is studied experimentally. The measurements were performed for microwave networks simulating quantum graphs. One and two ports measurements of the scattering matrix Ŝ necessary for determining c(x) were realized for the networks possessing 5 and 6 vertices, respectively. The network with six vertices was fully connected. In the case of the networks with five vertices, additionally to the fully connected configuration, we measured the networks without the bond connecting input/output vertices. The obtained experimental results besides the autocorrelation function of level velocities, also the nearest-neighbor spacing distribution and parametric velocities distribution are compared to the predictions of random matrix theory and numerical results.
We present the results of experimental study of the distribution P(R) of the reflection coefficient R and the distributions of Wigner's reaction K matrix for irregular, tetrahedral microwave graphs (networks) in the presence of absorption. Our experimental results are in good agreement with the exact theoretical predictions of Savin et al.
An introduction into the area of inverse problems for the Schrödinger operators on metric graphs is given. The case of metric finite trees is treated in detail with the focus on matching conditions. For graphs with loops we show that for almost all matching conditions the potential on the loop is not determined uniquely by the Titchmarsh-Weyl function. The class of all admissible potentials is characterized.
We analyze the echo dynamics in quasi-one-dimensional random media to investigate how the transition from localization to delocalization is encoded in its temporal decay properties. Our analysis extends from the standard perturbative regime corresponding to small perturbations (with respect to the mean level spacing) in the echo dynamics, out to the Wigner decay regime. On the theoretical side, our results rely on a banded random matrix modeling, and show in the localized regime under small perturbations a novel decay of the fidelity (Loschmidt echo), differing from the typical Gaussian decay seen within both diffusive and chaotic systems. For larger perturbation strengths, typical Wigner exponential decays are observed. Scattering echo measurements are performed experimentally within a quasi-1D microwave cavity randomly populated with point-like scatterers. Agreements are observed between experiments, numerics, and theoretical predictions.
Quantum graphs having one cycle are considered. It is shown that if the cycle contains at least three vertices, then the potential on the graph can be uniquely reconstructed from the corresponding Titchmarsh-Weyl function (Dirichlet-to-Neumann map) associated with graph's boundary, provided certain non-resonant conditions are satisfied.
The derivation of the virial theorem is presented both in classical and quantum mechanical approach. The kinetic energy and potential energy of the mechanical energy is converted to each other due to the virial theorem. Some of the different potentials are considered. For some of these potentials, the wavefunctions and energy eigenvalues of the Schrödinger Equation are derived.
The relativistic problem of spin-1/2 particles subject to the Woods-Saxon potential is investigated by using the functional analysis method. We obtain scattering and bound state solutions of the one-dimensional Dirac equation with the Woods-Saxon potential in terms of the Jacobi polynomials. We also calculated the transmission and reflection coefficients by using behavior of the wave functions at infinity.
We study the scattering of torsional waves through a quasi-one-dimensional cavity both from the experimental and theoretical points of view. The experiment consists of an elastic rod with square cross-section. In order to form a cavity, a notch at a certain distance of one end of the rod was grooved. To absorb the waves, at the other side of the rod, a wedge, covered by an absorbing foam, was machined. In the theoretical description, the scattering matrix S of the torsional waves was obtained. The distribution of S is given by Poisson's kernel. The theoretical predictions show an excellent agreement with the experimental results. This experiment corresponds, in quantum mechanics, to the scattering by a delta potential, in one dimension, located at a certain distance from an impenetrable wall.
Recently, it has been shown that the change of resonance widths in an open system under a perturbation of its interior is a sensitive indicator of the nonorthogonality of resonance states. We apply this measure to quantify parametric motion of the resonances. In particular, a strong redistribution of the widths is linked with the maximal degree of nonorthogonality. Then for weakly open chaotic systems we discuss the effect of spectral rigidity on the statistical properties of the parametric width shifts, and derive the distribution of the latter in a picket-fence model with equidistant spectrum.
We discuss lower and upper estimates for the spectral gap of the Laplace operator on a finite compact connected metric graph. It is shown that the best lower estimate is given by the spectral gap for the interval with the same total length as the original graph. An explicit upper estimate is given by generalizing Cheeger's approach developed originally for Riemannian manifolds.
Wave scattering in chaotic systems with a uniform energy loss (absorption) is considered. Within the random matrix approach we calculate exactly the energy correlation functions of different matrix elements of impedance or scattering matrices for systems with preserved or broken time-reversal symmetry. The obtained results are valid at any number of arbitrary open scattering channels and arbitrary absorption. Elastic enhancement factors (defined through the ratio of the corresponding variance in reflection to that in transmission) are also discussed.
In this note we explain the method how to find the resonance condition on quantum graphs, which is called pseudo-orbit expansion. In three examples with standard coupling we show in detail how to obtain the resonance condition. We focus on non-Weyl graphs, i.e. the graphs which have fewer resonances than expected. For these graphs we explain benefits of the method of "deleting edges" for simplifying the graph.
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