  We describe here the construction and characterization of a high-resolution
optical magnetometer to measure the full vector magnetic field on an ultrathin
layer near the surface of the device. This solid-state device is based on
quantum sensors created by a layer of nitrogen-vacancy (NV) centers less than
20 nm below the surface of an ultrapure diamond. This ensemble of nanosensors
provides a versatile device capable of mapping magnetic fields and surface
current densities with a sub-micrometer resolution and high sensitivity, making
it suitable for many applications. Here, we show a custom-built prototype to
demonstrate an operating proof-of-concept device.
