Dynamics of complex physical systems

Dnr:

SNIC 2018/3-237

Type:

SNAC Medium

Principal Investigator:

Claude Dion

Affiliation:

Umeå universitet

Start Date:

2018-05-01

End Date:

2018-11-01

Primary Classification:

10302: Atom and Molecular Physics and Optics

Secondary Classification:

10399: Other Physics Topics

Webpage:

- Kebnekaise at HPC2N: 20 x 1000 core-h/month

This project covers the study of different physical systems, based on substantially different principles, from quantum mechanics to fluid dynamics. The main unifying theme is their dynamical (time-dependent) aspect, along with the fact that they are computationally intensive. The reason for grouping them in a single application is simply that they correspond to different research projects I am involved in in parallel.
The first part concerns the simulation of the dynamics of molecular ions in electrostatic traps, such as the Paul trap. I am interested in particular in the rotation of these molecular ions, and how the presence of a permanent dipole moment affects the motion of the ion in the trap, as well as how rotation is affected by the trapping field. Trapped ions are currently used in experiments aimed at developing quantum information processing and high-precision spectroscopy, and an investigation of the quantum dynamics of the ions in the trap, and its eventual control using laser fields, will be of great interest to these fields. The simulations used here are based on the time-dependent Schrödinger equations, where a semi-classical method is used to reduce the computational requirements that a fully quantum mechanical approach would require.
The second part is aimed at the study the behavior of dilute gases of cold atoms at temperatures below the millikelvin. The project concerns the dynamics of atoms in optical lattices, which are spatially-modulated potentials created from the interference of laser beams. The objective here is to get a time-dependent picture of atoms trapped in optical lattices and to look for anomalous statistics in the distribution of high-momentum atoms. In addition, the effect of gravity, which corresponds here to a tilt of the optical lattice potential, is studied. The atom + optical lattice system can be related to a very general problem in physics, that of a Brownian particle moving in a periodic potential, and one of the aims of this work is to see how the actual experimental setup can be used as an actual implementation of the system and, therefore, as a testbed for fundamental statistical physics. The simulations consists in solving the Fokker-Planck equation for a single atom in a lattice, in a semi-classical approach, where only the internal state of the atom is treated quantum-mechanically.
A third part of the project concerns the dynamics of combustion in premixed gases. In particular, we simulate the propagation of frame fronts in narrow tubes, looking at different aspects such as the acceleration of the flame front, its curvature, the development of instabilities and the deflagration to detonation transition. Current work focuses mainly on the role of cold tube walls on flame acceleration and the effect of obstacles. The dynamics are obtained by solving the Navier-Stokes combustion equations.