Estimation of Imbert-Fedorov shifts based on SU(1,1) interferometer breaking through the shot-noise limit
Phys. Rev. A 111, 062615 – Published 16 June, 2025
DOI: https://doi.org/10.1103/jb26-qws1
Abstract
Imbert-Fedorov (IF) shifts refer to transverse tiny displacements of light beams at the interface of two media. Since the IF shifts are a reflection of the light-matter interaction, they can be applied to sense the properties of the medium or light beam. To evaluate the errors of parameters in various kinds of sensors with high precision, quantum metrology based on the SU(1,1) interferometer is expected to improve the measurement accuracy beyond the shot-noise limit (SNL). We propose a theoretical scheme to investigate the IF shifts and incident angle sensitivity for a Laguerre-Gauss beam by introducing a surface-plasmon-resonance (SPR) sensor into the SU(1,1) interferometer. We derived the sensitivity of the IF shifts and incident angle based on the homodyne detection. Meanwhile, the quantum Cramér-Rao bound and SNL of IF shifts and incident angle are obtained in our scheme. Our results demonstrate that the sensitivity of both IF shifts and incident angle can break through the SNL around the SPR angle by injecting two coherent states with large coherent amplitude. Furthermore, it is possible to get the maximal IF shifts and the optimal IF shifts sensitivity simultaneously on the two sides of the SPR angle. Our scheme provides a method for measuring tiny beam shifts and small angular displacement in SPR sensors. The results can be helpful for the development of quantum metrology based on quantum sensors and a deep understanding of light-matter interactions.
