While elementary processes at the atomic and molecular scale are intrinsically quantum mechanical in nature, it is well known that molecular motions in many-body systems can often be considered as classical for all practical purposes. Hence, Molecular Dynamics (MD) simulations based entirely upon classical mechanics are without any doubt the key simulation tool for complex biological and material systems. This is the result of classical-limit behavior of the nuclear motions, as well as loss of phase coherence at the ensemble level, and the dynamical loss of coherence due to rapid decoherence effects induced by the ubiquitous coupling to an environment.

However, with the advent of spectroscopic techniques that monitor chemical and biochemical processes on ultrafast - femtosecond to picosecond - time scales, the coherent quantum (wavepacket) character of molecular motions can be monitored selectively, before the transition to an ensemble state sets in. Over the past few years, it has become increasingly clear that such photoinduced processes may preserve their coherent quantum nature for timescales in the picosecond range and beyond, even when coupled to an environment. This applies both to "simple" environments (like solvents) and complex biological environments (like proteins). In particular, recent experiments have brought clear evidence that excitonic coherence (entanglement) plays a key role in energy transfer in photosynthetic antenna systems and semiconducting polymers [I1-I5]. This has raised the question whether the conventional picture of emergent classical, macroscopic behavior necessarily holds on the time and length scales that are decisive for biological function.

Against this background, the understanding of the quantum-classical boundary, and the transition from quantum to classical behavior is essential both from a fundamental and a practical, applied viewpoint. The present school seeks to address these issues from the combined viewpoint of dissipation theory [G1,G7], statistical approaches [G4,I5], and semiclassical and mixed quantum-classical theories [G2,G5,G8-G10]. The decoherence phenomenon [G1-G4,G10,G13] will naturally result as one of the central themes. A particular focus will be placed on the non-Markovian regime where standard Markovian master equations ("fast fluctuation'' case) cannot be employed [G1,G7]. Various theoretical approaches as well as numerical techniques and algorithms will be presented and discussed.

This School is planned as a joint project of CECAM and the COST Action MP1006 ("Fundamental Problems of Quantum Physics"). We aim to provide young researchers with a thorough understanding of the dynamics of high-dimensional quantum systems, the role of dissipation and decoherence, and emergent classicality. This formal and conceptual background will be combined with numerical applications in the area of quantum and quantum-classical simulations. This combination can be realized in a unique way by a combined CECAM/COST project.

The venue is the University of Rome "La Sapienza" which will provide appropriate lecture rooms as well as a computer lab.