Quantum Enhanced Probes of Magnetic Circular Dichroism

AbstractMagneto‐optical microscopies, including optical measurements of magnetic circular dichroism, are increasingly ubiquitous tools for probing spin‐orbit coupling, charge‐carrier g‐factors, and chiral excitations in matter, but the minimum detectable signal in classical magnetic circular dichroism measurements is fundamentally limited by the shot‐noise limit of the optical readout field. Here, a two‐mode squeezed light source is used to improve the minimum detectable signal in magnetic circular dichroism measurements by 3 decibels compared with state‐of‐the‐art classical measurements, even with relatively lossy samples like terbium gallium garnet. These results provide a framework for new quantum‐enhanced magneto‐optical microscopies that are particularly critical for environmentally sensitive materials and for low temperature measurements where increased optical power can introduce unacceptable thermal perturbations.