F. Aigner

Shot Noise in the Chaotic-to-Regular Crossover Regime

We investigate the shot noise for phase-coherent quantum transport in the chaotic-to-regular crossover regime. Employing the modular recursive Greens function method for both ballistic and disordered two-dimensional cavities, we find the Fano factor and the transmission eigenvalue distribution for regular systems to be surprisingly similar to those for chaotic systems. We argue that, in the case of regular dynamics in the cavity, diffraction at the lead openings is the dominant source of shot noise. We also explore the onset of the crossover from quantum-to-classical transport and develop a quasiclassical transport model for shot noise suppression which agrees with the numerical quantum data.

Fast-atom diffraction at surfaces

Fast helium atoms diffracted at alkali-halide surfaces under grazing angles of incidence exhibit intriguing diffraction patterns. The persistence of quantum coherence is remarkable, considering high surface temperatures and high (keV) kinetic energies of the incident atoms. Dissipative and decohering effects such as the momentum transfer between the incident helium atoms and the surface influence the diffraction patterns and control the width of the diffraction peaks, but they are weak enough to preserve the visibility of the diffration patterns. We perform an ab initio simulation of the quantum diffraction of fast helium beams at a LiF (100) surface in the (110) direction. Our results agree well with recent experimental diffraction data.

Influence of inelastic processes on fast-atom-surface diffraction

Diffraction of fast helium atoms at alkali-halide surfaces under grazing angles of incidence shows intriguing diffraction patterns. The persistence of quantum coherence is remarkably strong, even though high surface temperatures and high (keV) kinetic energies of the incident atoms would strongly suggest the dominance of dissipative and decohering processes. The main source of decoherence is the excitation or absorption of surface vibrations upon impact. The momentum transfer between the surface and the incident helium atom depends on the amplitude of the thermal vibrations of the surface atoms and the energy of the incident particle. We present an ab initio simulation of the quantum diffraction of fast helium beams at a LiF (100) surface in the (110) direction, and compare with recent experimental diffraction data.

Chaotic‐to‐regular crossover of shot noise in mesoscopic conductors

We study the shot noise by numerically simulating phase‐coherent transport through a quantum dot. The chaotic‐to‐regular crossover regime of shot noise suppression is investigated explicitly by tuning the disorder potential and the openings of the dot. Employing the Modular Recursive Green’s Function Method we obtain results for the Fano factor in regular systems which show a remarkable similarity to the results in chaotic systems. We argue that in the absence of chaotic scattering diffraction at the lead openings is the dominant source of shot noise. Estimates for the shot noise induced by this mechanism are presented, which agree with the numerical data.

A modular method for the efficient calculation of ballistic transport through quantum billiards

We present a numerical method which allows to efficiently calculate quantum transport through phase-coherent scattering structures, so-called “quantum billiards”. Our approach consists of an extension of the commonly used Recursive Greens Function Method (RGM), which proceeds by a discretization of the scattering geometry on a lattice with nearest-neighbour coupling. We show that the efficiency of the RGM can be enhanced considerably by choosing symmetry-adapted grids reflecting the shape of the billiard. Combining modules with different grid structure to assemble the entire scattering geometry allows to treat the quantum scattering problem of a large class of systems very efficiently. We will illustrate the computational challenges involved in the calculations and present results that have been obtained with our method.