Surpassing the Standard Quantum Limit for Optical Imaging Using Nonclassical Multimode Light

TLDR

The study demonstrates that continuous‑wave superposition of spatial modes enables displacement measurement of a light beam below the standard quantum limit. Multimode squeezed light is produced by mixing a vacuum‑squeezed beam with a spatially orthogonal coherent beam. The resulting beam, though not squeezed, exhibits strong internal spatial correlations, allowing its position to be measured with a split detector more precisely than a classical beam, thereby improving sensitivity for small displacement measurements.

Abstract

Using continuous wave superposition of spatial modes, we demonstrate experimentally displacement measurement of a light beam below the standard quantum limit. Multimode squeezed light is obtained by mixing a vacuum squeezed beam and a coherent beam that are spatially orthogonal. Although the resultant beam is not squeezed, it is shown to have strong internal spatial correlations. We show that the position of such a light beam can be measured using a split detector with an increased precision compared to a classical beam. This method can be used to improve the sensitivity of small displacement measurements.