Accuracy in the measurement of magnetic fields using nitrogen-vacancy centers in nanodiamonds

We have measured 10 and 20 mT magnetic fields using NV centers in nanodiamonds and have demonstrated that the accuracy of these measurements is about 20 [mu]T. This value is an order of magnitude larger than the precision defined by random fluctuations in the measurements. The presented analysis indicates that the 20 [mu]T systematic errors at such fields are intrinsic to the nanodiamonds. The possible reason for this error is coupling of NV centers with paramagnetic entities in the nanodiamonds such as other NV centers, super(13) C, and super(14) N nuclei.