Quenching spin decoherence in diamond through spin bath polarization

We experimentally demonstrate that the decoherence of a spin by a spin bath can be completely eliminated by fully polarizing the spin bath. We use electron paramagnetic resonance at 240 GHz and 8 T to study the electron-spin coherence time T(2) of nitrogen-vacancy centers and nitrogen impurities in diamond from room temperature down to 1.3 K. A sharp increase of T(2) is observed below the Zeeman energy (11.5 K). The data are well described by a suppression of the flip-flop induced spin bath fluctuations due to thermal electron-spin polarization. T(2) saturates at similar to 250 mu s below 2 K, where the polarization of the electron-spin bath exceeds 99%.