  The quantum Zeno effect, i.e. the inhibition of coherent quantum dynamics by
projective measurements is one of the most intriguing predictions of quantum
mechanics. Here we experimentally demonstrate the quantum Zeno effect by
inhibiting the microwave driven coherent spin dynamics between two ground state
spin levels of the nitrogen vacancy center in diamond nano-crystals. Our
experiments are supported by a detailed analysis of the population dynamics via
a semi-classical model.
