Entangled Light Enabled Quantum Magnetic Gradiometer

We present a quantum magnetic gradiometer that achieves sub-shot-noise sensitivity through the use of entangled twin beams and differential detection. Benefiting from large quantum enhancement, high common-mode rejection ratio, and best sensitivity ever observed in magnetometry with squeezed light, the developed quantum gradiometer opens up new possibilities for utilizing quantum-enhanced technology in the development of sensitive magnetometry for practical applications in noisy and physically demanding environments.