Magneto‐Optical Sensing Beyond the Shot Noise Limit

Magneto-optical sensors including spin noise spectroscopies and magneto-optical Kerr effect microscopies are now ubiquitous tools for materials characterization that can provide new understanding of dynamics, hyperfine interactions, spin-orbit charge-carrier g-factors. Both interferometric intensity-difference measurements photon shot-noise limited sensitivity, but further improvements in sensitivity with classical resources require either increased laser power induce unwanted heating electronic perturbations or measurement times obscure out-of-equilibrium dynamics radically slow experimental throughput. Proof-of-principle have already demonstrated quantum enhanced a squeezed readout field likely to be critical the non-perturbative excitations emerge at low temperatures. Here, we propose truncated nonlinear low-temperature is accessible today's optical resources. We show 10 $\text{nrad}/\sqrt{\text{Hz}}$ achievable as small 1 $\mu$W such realistic $T$ = 83 mK maintained commercially available dilution refrigerators. The advantage proposed persists even limit large loss squeezing parameters.