The Advances series highlights recent developments in atomic, molecular and optical physics. Readers can learn about recent advances from articles that are comprehensive in nature. These articles often contain background material and extensive references; as such they can serve as useful source material for many years to come. The articles are written by experts in their fields Most articles offer readers the opportunity to learn about recent advances in atomic, molecular, and optical physics. Since there are only modest restrictions on the length of the contributions, authors have the ability to develop the subject matter in a clear fashion