Computational physics

The principal aim of the research group Computational Physics is to conduct research through the innovative use of computer and information technology. For our simulation work we use PCs, the IBM BlueGene/P at the RuG, and the supercomputer of the National Supercomputer Facilities in Amsterdam and the supercomputers of the Jülich Supercomputing Centre. For detailed information about the group, visit www.compphys.org.

Event-by-event simulation of quantum phenomena (work done in collaboration with the Institute for Advanced Simulation, Jülich Supercomputing Centre/Univ. Aachen, Department of Physics, University of Tokyo, Institute of Molecules and Materials, Radboud University of Nijmegen)

A few years ago, we proved that there exist classical, locally causal, deterministic (or probabilistic) and event-based processes which behave, in all respects, like quantum systems. This idea is further confirmed by our recent work that demonstrates that is possible to reproduce the results of various kinds of interference phenomena and of for instance, Einstein-Podolsky-Rosen-Bohm experiments, without recourse to concepts of quantum theory. We also showed that this approach can be generalized to simulate universal quantum computation by a deterministic event-by-event process. As universal quantum computers are, in principle, capable of simulating any quantum system, the logical conclusion is that the method we have proposed can simulate wave interference phenomena and many-body quantum systems using classical, particle-like processes only. We extended the list of successful demonstrations by applications to the quantum eraser, the delayed choice and the Hanbury Brown-Twiss experiments, showing that interference and full which-way information can co-exist. Most importantly, we also constructed a particle-only model for double-slit experiments with single-photons that reproduce the results of wave theory without making any reference to the latter. For the first time, we also succeeded to prove rigorously that our simulation model contains Maxwell’s theory as a limiting case. More information and demos can be found at www.compphys.net.

Nanoscale magnetism (work done in collaboration with the Department of Physics, University of Tokyo, Institute of Molecules and Materials, Radboud University of Nijmegen)

One thread of research focused on the fundamental question if and how the dynamical evolution of a system that is brought in contact with another dynamical system (the environment) drives the former to thermal equilibrium. This question, which dates back to the early days of the development of statistical physics, remains elusive up to this day. In fact, it has become tradition to simply postulate that the two systems establish some thermal equilibrium. For the first time, we have shown that such a dynamical process actually exists. Surprisingly, we succeeded to demonstrate this within the realm of quantum systems.Computer simulations of fairly generic models of magnetic systems showed that the thermal equilibrium is established in a two-step process. First there is a stage in which the system looses all phase coherence (decoherence) and then a stage in which the state of the system relaxes to its canonical distribution.