  In this Letter, we proposed and experimentally demonstrated a method to
detect vector magnetic field with a single nitrogen vacancy (NV) center in
diamond. The magnetic field in parallel with the axis of the NV center can be
obtained by detecting the electron Zeeman shift, while the Larmor precession of
an ancillary nuclear spin close to the NV center can be used to measure the
field perpendicular to the axis. Experimentally, both the Zeeman shift and
Larmor precession can be measured through the fluorescence from the NV center.
By applying additional calibrated magnetic fields, complete information of the
vector magnetic field can be achieved with such a method. This vector magnetic
field detection method is insensitive to temperature fluctuation and it can be
applied to nanoscale magnetic measurement.
