Abstract

We experimentally demonstrate that a squeezed probe optical field can improve the sensitivity of magnetic field measurements based on nonlinear magneto-optical rotation (NMOR) with an amplitude-modulated pump when compared to a coherent probe field under identical conditions. To realize an all-atomic magnetometer prototype, we utilize a nonlinear atomic interaction, known as polarization self-rotation, to produce a squeezed probe field. An independent pump field, amplitude-modulated at the Larmor frequency of the bias magnetic field, allows us to extend the range of most sensitive NMOR measurements to sub-Gauss magnetic fields. While the overall sensitivity of the magnetometer is rather low (${\gt}250 \;{\rm{pT}}/\sqrt {{\rm{Hz}}}$), we clearly observe a $15 \%$ sensitivity improvement when the squeezed probe is used. Our observations confirm the recently reported quantum enhancement in a modulated atomic magnetometer [Phys. Rev. Lett. 127, 193601 (2021) [CrossRef]  ].

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