Controlling the interaction of a single quantum system with its environment
is a fundamental challenge in quantum science and technology. We dramatically
suppress the coupling of a single spin in diamond with the surrounding spin
bath by using double-axis dynamical decoupling. The coherence is preserved for
arbitrary quantum states, as verified by quantum process tomography. The
resulting coherence time enhancement is found to follow a general scaling with
the number of decoupling pulses. No limit is observed for the decoupling action
up to 136 pulses, for which the coherence time is enhanced more than 25 times
compared to spin echo. These results uncover a new regime for experimental
quantum science and allow to overcome a major hurdle for implementing quantum
information protocols.Comment: submitted 24 May 2010; published online 9 September 201