The spin degree-of-freedom is o?ering a wide range of intriguing oppor- nities both in fundamental as well as in applied solid-state physics. When combined with the rich and fertile physics of low-dimensional semicondu- ingstructuresandwiththepossibilitytochange, forexample, carrierdensity, electric ?elds or coupling to other quantum systems in a controlled way, an extremely exciting and interesting research ?eld is opened. Most comm- cial electronic devices are based on spin-independent charge transport. In the last two decades, however, scientists have been focusing on the ambitious...