Magneto-optical spectroscopies are increasingly powerful probes of spin excitations in quantum materials, but at cryogenic temperatures, the laser excitation can be highly non-perturbative. While balanced photodetection can be used to suppress classical noise sources, the photon shot noise limit fundamentally constrains the measurement sensitivity for a given laser power. Here, we have used a two-mode squeezed light source to suppress noise below the shot noise level for magnetic circular dichroism measurements, thus enabling lower power measurements with reduced photothermal effects. We also describe the fundamental sensitivity limits for quantum enhanced interferometric and intensity-difference magneto-optical Kerr effect and circular dichroism spectroscopies.
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