An ensemble of nitrogen-vacancy (NV) centers in diamond is an attractivedevice to detect small magnetic fields. In particular, by exploiting the factthat the NV center can be aligned along one of four different axes due tosymmetry, it is possible to extract information concerning vector magneticfields. However, in the conventional scheme, low readout contrasts of the NVcenters significantly decrease the sensitivity of the vector magnetic fieldsensing. Here, we propose a way to improve the sensitivity of the vectormagnetic field sensing of the NV centers using multi-frequency control. Sincethe Zeeman energy of the NV centers depends on the direction of the axis, wecan independently control the four types of NV centers using microwave pulseswith different frequencies. This allows us to use every NV center for thevector field detection in parallel, which effectively increases the readoutcontrast. Our results pave the way to realize a practical diamond-based vectorfield sensor.
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