Associated Professor Lecture: Quantum non-adiabatic processes

by Dr Åsa Larson (Stockholms Universitet)

Friday 12 Jun 2009, 13:00 → 15:00 Europe/Stockholm

FA31

The adiabatic theorem is a central concept dating back to the early years of quantum mechanics. In its original formulation it was stated that the system remains in its instantaneous eigenstate provided that the time-dependence of the Hamiltonian varies slowly enough and that the energy eigenlevel is well eparated from the nearby levels of the spectrum. As a onsequence of the breakdown of this theorem, non-adiabatic effects become important and I will discuss these here. Such processes are extremely relevant since they lead to a change of state of the system. Non-adiabatic effects lie behind various phenomena in many multidisciplinary areas of physics, chemistry and biology. In this talk, I will demonstrate the role of non-adiabatic effects in quantum optics, solid state physics, atomic physics, molecular physics and chemistry. A simple time-dependent two-level Hamiltonian will be discussed for which analytical solutions exist. These models can be applied to describe the non-adiabatic effects occurring in the areas just mentioned. The non-adiabaticity of a process may originate from an explicit time-dependence of the Hamiltonian, by particle motions or by some variation of external parameters such as a magnetic field. In the field of molecular physics and chemistry, the adiabatic theorem is related to the Born-Oppenheimer approximation which is the foundation for the separation of the electronic and nuclear motions. For a multidimensional system, conical intersections occur where the nonadiabatic interactions may become infinite. These intersections are more common in nature than previously believed and they play a crucial role in many chemical reactions.