Estimating IF shifts based on SU(1,1) interferometer

Abstract

IF (Imbert--Fedorov) shifts which refers to a transverse micro-displacement occurs at the interface between two media. The estimation of such micro-displacement enables a deeper understanding of light-matter interactions. In this paper, we propose a theoretical scheme to investigate the IF shifts and incident angle sensitivity by introducing SPR sensor into the SU(1,1) interferometer. By injecting two coherent states in the SU(1,1) interferometer, we obtain the sensitivity of the IF shifts and incident angle based on the homodyne detection. Our results demonstrate that it is possible to get the maximal IF shift and the optimal IF shifts sensitivity simultaneously. Meanwhile, the orbit angular momentum carried by Laguerre-Gauss (LG) beam is unfavorable for improving the IF shift sensitivity. Furthermore, we have investigated the sensitivity of the incident angle in our scheme and found that it is capable of surpassing the sensitivity limit of $(6\times 10^{-6}){{}^\circ}$. This allows us to achieve a more precise IF shifts sensitivity than the traditional weak measurement method used for IF shift detection, which typically has a rotation precision limit of 0.04${{}^\circ}$ [Journal of Optics, 19(10), 105611]. More importantly, both the sensitivity of IF shifts and incident angle can breakthrough the (shot noise limit) SNL, even approaching the Cramér-Rao bound (QCRB) at the incident angle $θ=43.6208{{}^\circ}$ and $θ=43.6407{{}^\circ}$. We also discover that increasing the coherent amplitude is beneficial for improving the sensitivity of both the IF shifts and incident angle. Our findings shall offer a novel scheme for measuring micro-displacement in SPR sensor. These results can be helpful in the development of more precise quantum-based sensors for studying light-matter interactions.