Lateral drag of spin coherence in gallium arsenide

The importance of spin-transport phenomena in condensed-matter physics has increased over the past decade with the advent of metallic giant-magnetoresistive systems and spin-valve transistors(1). An extension of such phenomena to semiconductors should create possibilities for seamless integration of 'spin electronics' with existing solid-state devices, and may someday enable quantum computing schemes using electronic spins as non-local mediators of coherent nuclear spin interactions(2). But to realize such goals, spin transport must be effected without destroying the relevant spin information. Here we report time-resolved optical studies of non-local Faraday rotation in n-type bulk gallium arsenide, which show macroscopic lateral transport of coherently precessing electronic spins over distances exceeding 100 micrometres. The ability to drag these spin packets by their negative charge, without a substantial increase in spin decoherence, is a consequence of the rather weak entanglement of spin coherence with orbital motion in this system(3).