  We present a theoretical study of the anisotropy of the spin relaxation and
decoherence in typical quantum wells with an arbitrary magnetic field. In such
systems, the orientation of the magnetic field relative to the main
crystallographic directions is crucial, owing to the lack of spin-rotation
symmetry. For typical high mobility samples, relaxation anisotropies in the
motional narrowing limit owing to the interplay of Rashba and Dresselhaus spin
orbit coupling are calculated. We also include the effect of the
cubic-in-momentum terms. Although commonly ignored in literature, the latter
were experimentally evidenced by the observation of strong anisotropy in spin
decoherence measurements by different experimental groups and has long remained
unexplained.
