Scientists in Germany and Canada have developed a new technique called ballistic spin resonance that is a step forward for controlling spin in semiconductors and has implications for quantum computing.

Electron spin resonance describes the flipping of spin in unpaired electrons (also called radicals). Inducing electron spin resonance using high-frequency magnetic fields has made the study of quantum mechanics possible. It is a valuable tool because the magnetic field can be used to control transitions between the spin state of unpaired electrons. Spin can also be induced using high-frequency electric fields in certain materials; the oscillation of the electrons itself creates a magnetic field that can act on the electrons' spin. Previous studies using external electric fields have been successful in flipping spins in a number of materials, including two-dimensional gases of electrons and 'quantum dots'. The problem is that oscillating fields are actually cumbersome to generate on a chip.

Dr Sergey Frolov of the University of British Columbia in Canada and colleagues in Germany took an original approach, which is highly desirable for electronic applications. The new 'ballistic spin resonance' involves making electrons bounce back and forth in the tiny channels of a two-dimensional semiconductor. Spin resonance is achieved using the magnetic field that is produced as an interaction between the electrons' spin and their orbit. The repeated bouncing of the electrons off the channel walls effectively makes the magnetic field oscillate. The frequency of this oscillation happens to be valuable for spin-resonance applications.

Dr Lieven Vandersypen of Delft University of Technology in the Netherlands notes: 'In the future, one could imagine applying the authors' technique of flipping spins to entire solid-state electronic circuits in which information is encoded in the spin state of the electrons. This is the vision of the field of spintronics, which has already led to discoveries such as "giant magnetoresistance" and the subsequent miniaturisation of hard-disk drives.'

By Vasil Sidorov on April 20, 2009   after Nature    www.nature.com