M. Bonitz - Academia.edu (original) (raw)

Papers by M. Bonitz

Physical Review E

Ultrafast relaxation and correlation buildup in an N-particle system can be described theoretical... more Ultrafast relaxation and correlation buildup in an N-particle system can be described theoretically using two completely different methods: mechanical equations of motion ͑molecular dynamics͒ and quantum-statistical models ͑Kadanoff-Baym equations͒. We propose to perform detailed quantitative comparisons of the two methods to obtain a powerful and unbiased tool for testing different approximations. Results of such comparison are presented for a weakly coupled electron gas, which show remarkable agreement.

AIP Conference Proceedings, 2002

The results of numerical simulation of strongly coupled hydrogen plasma are presented. Direct fer... more The results of numerical simulation of strongly coupled hydrogen plasma are presented. Direct fermionic path-integral Monte-Carlo method is used for calculations. It allows one to compute pressure, energy, and pair distribution functions of hydrogen plasma over a wide range of densities and temperatures. AtT= 10 4 K and density range 0.1-1.5 g/cc phase transition which vanishes at higher temperatures is predicted. This density range covers the region of abrupt increase of an electrical conductivity under shock compression experiments.

Physical Review B, 2002

The quantum dynamics of an ensemble of interacting electrons in an array of random scatterers is ... more The quantum dynamics of an ensemble of interacting electrons in an array of random scatterers is treated using a new numerical approach for the calculation of average values of quantum operators and time correlation functions in the Wigner representation. The Fourier transform of the product of matrix elements of the dynamic propagators obeys an integral Wigner-Liouville-type equation. Initial conditions for this equation are given by the Fourier transform of the Wiener path integral representation of the matrix elements of the propagators at the chosen initial times. This approach combines both molecular dynamics and Monte Carlo methods and computes numerical traces and spectra of the relevant dynamical quantities such as momentum-momentum correlation functions and spatial dispersions. Considering as an application a system with fixed scatterers, the results clearly demonstrate that the many-particle interaction between the electrons leads to an enhancement of the conductivity and spatial dispersion compared to the noninteracting case.

Physical Review B, 2015

We analyze the superfluid phase transition of harmonically confined bosons with long-range intera... more We analyze the superfluid phase transition of harmonically confined bosons with long-range interaction in both two and three dimensions in a broad parameter range from weak to strong coupling. We observe that the onset of superfluidity occurs in 3D at significantly lower temperatures compared to 2D. This is demonstrated to be a quantum degeneracy effect. In addition, the spatial distribution of superfluidity across the shells of the clusters is investigated. It is found that superfluidity is substantially reduced in the outer layers due to increased correlation effects.

New Journal of Physics, 2013

ABSTRACT The spectral properties of three-dimensional dust clusters confined in gaseous discharge... more ABSTRACT The spectral properties of three-dimensional dust clusters confined in gaseous discharges are investigated using both a fluid mode description and the normal mode analysis (NMA). The modes are analysed for crystalline clusters as well as for laser-heated fluid-like clusters. It is shown that even for clusters with low particle numbers and under presence of damping fluid modes can be identified. Laser-heating leads to the excitation of several, mainly transverse, modes. The mode frequencies are found to be nearly independent of the coupling parameter and support the predictions of the underlying theory. The NMA and the fluid mode spectra demonstrate that the wakefield attraction is present for the experimentally observed Yukawa balls at low pressure. Both methods complement each other, since NMA is more suitable for crystalline clusters, whereas the fluid modes allow to explore even fluid-like dust clouds.

physica status solidi (b), 1998

ABSTRACT

Condensed Matter Physics, 2004

A quantum kinetic theory for weakly inhomogeneous charged particle systems is derived within the ... more A quantum kinetic theory for weakly inhomogeneous charged particle systems is derived within the framework of nonequilibrium Green's functions. The results are of relevance for valence electrons of metal clusters as well as for confined Coulomb systems, such as electrons in quantum dots or ultracold ions in traps and similar systems. To be specific, here we concentrate on the application to metal clusters, but the results are straightforwardly generalized. Therefore, we first give an introduction to the physics of correlated valence electrons of metal clusters in strong electromagnetic fields. After a brief overview on the jellium model and the standard density functional approach to the ground state properties, we focus on the extension of the theory to nonequilibrium. To this end a general gauge-invariant kinetic theory is developed. The results include the equations of motion of the two-time correlation functions, the equation for the Wigner function and an analysis of the spectral function. Here, the concept of an effective quantum potential is introduced which retains the convenient local form of the propagators. This allows us to derive explicit results for the spectral function of electrons in a combined strong electromagnetic field and a weakly inhomogeneous confinement potential.

Physical review. E, Statistical, nonlinear, and soft matter physics, 2001

Classical Molecular Dynamics simulations for a one-component plasma are presented. Quantum effect... more Classical Molecular Dynamics simulations for a one-component plasma are presented. Quantum effects are included in the form of the Kelbg potential. Results for the dynamical structure factor are compared with the Vlasov and random phase approximation theories. The influence of the coupling parameter Gamma, degeneracy parameter rho Lambda(3), and the form of the pair interaction on the optical plasmon dispersion is investigated. An improved analytical approximation for the dispersion of Langmuir waves is presented.

Physical Review E, 1999

The Kadanoff-Baym equations (KBE) are usually derived under the assumption of the weakening of in... more The Kadanoff-Baym equations (KBE) are usually derived under the assumption of the weakening of initial correlations (Bogolyubov's condition) and, therefore, fail to correctly describe the short time behavior. We demonstrate that this assumption is not necessary. Using functional derivatives techniques, we present a straightforward generalization of the KBE which allows to include arbitrary initial correlations and which is more general than previous derivations. As a result, an additional collision integral is obtained which is being damped out after a few collisions. Our results are complemented with numerical investigations showing the effect of initial correlations.

Physics of Fluids B: Plasma Physics, 1993

The nonequilibrium properties of strongly coupled plasmas are investigated taking into account re... more The nonequilibrium properties of strongly coupled plasmas are investigated taking into account reaction and diffusion processes. The starting point is quantum kinetic equations for systems with chemical reactions involving many-body effects like screening, self-energy, and medium-dependent scattering. The influence of these effects on the kinetics of reaction and diffusion processes is discussed. Generalized expressions for the coefficients of impact ionization and diffusion are derived exhibiting a strong density dependence due to the manybody effects. Solving the reaction-diffusion equation (RDE) for a dense hydrogen plasma, nonlinear phenomena such as bistability, running ionization fronts, and droplet formation are obtained.

This chapter contains a brief introduction to the field of quantum simulations. Beginning with a ... more This chapter contains a brief introduction to the field of quantum simulations. Beginning with a numerical treatment of single-particle problems by exact numerical solution of the time-dependent Schrödinger equation , we demonstrate concepts useful in the computational treatment of quantum systems. These rather basic techniques are limited by the number of particles, N. Considering an increase of system size, approximation methods arising from many-particle theories are necessary. Here, we introduce two powerful approaches: the (time-dependent) Hartree-Fock method with improvements for inclusion of correlations based on nonequilibrium Green's functions and, for the calculation of time-independent phenomena, a rigorous quantum Monte Carlo technique. These computational tools complement each other and thus provide for a comprehensive theoretical modelling of quantum plasmas.

2008 IEEE 35th International Conference on Plasma Science, 2008

Strongly Coupled Coulomb Systems, 2002

With the development of femtosecond lasers, one is now able to create strongly correlated plasmas... more With the development of femtosecond lasers, one is now able to create strongly correlated plasmas in extreme nonequilibrium and probe its behavior with high time resolution. During the relaxation, interesting short-time phenomena occur, such as the build-up of ...

Plasma Sources Science and Technology, 2013

We propose and demonstrate a concept that mimics the magnetization of the heavy dust particles in... more We propose and demonstrate a concept that mimics the magnetization of the heavy dust particles in a complex plasma while leaving the properties of the light species practically unaffected. It makes use of the frictional coupling between a complex plasma and the neutral gas, which allows us to transfer angular momentum from a rotating gas column to a well-controlled rotation of the dust cloud. This induces a Coriolis force that acts exactly as the Lorentz force in a magnetic field. Experimental normal mode measurements for a small dust cluster with four particles show excellent agreement with theoretical predictions for a magnetized plasma.