Abstract: This disclosure relates to a magnetometer for measuring a magnetic field. The magnetometer comprises a solid state quantum system with at least two quantum spin states. A control signal generator sets the quantum system into a quantum state that accumulates a phase over time depending on the magnetic field. A detector measures a signal from the quantum system indicative of the accumulated phase at a measurement time after the setting of the quantum state. A processor determines a magnetic field measurement based on the signal measured by the detector. Importantly, the quantum system is mounted on a rotator that is configured to rotate the quantum system about a rotation axis that defines an angle with the direction of the magnetic field and at a rotation rate that modulates the magnetic field over the measurement time.