  Dynamical decoupling (DD) is an active and effective method for suppressing
decoherence of a quantum system from its environment. In contrast to the
nominal biaxial DD,this work presents a uniaxial decoupling protocol that
requires a significantly reduced number of pulses and a much lower bias field
satisfying the "magic" condition.We show this uniaxial DD protocol works
effectively in a number of model systems of practical interests, e.g., a spinor
atomic Bose-Einstein condensate in stray magnetic fields (classical noise), or
an electron spin coupled to nuclear spins (quantum noise) in a semiconductor
quantum dot. It requires only half the number of control pulses and a 10-100
times lower bias field for decoupling as normally employed in the above
mentioned illustrative examples,and the overall efficacy is robust against
rotation errors of the control pulses. The uniaxial DD protocol we propose
shines new light on coherent controls in quantum computing and quantum
information processing, quantum metrology, and low field nuclear magnetic
resonance.
