We have found that the error-signal frequency corresponding to the coherent population trapping resonance can be displaced from that of "$0-0$" transition unperturbed by the optical field, although the frequency is not sensitive to changes in its intensity. We consider the double $Λ$-system of levels interacting with the asymmetric polychromatic optical field to demonstrate that this effect arises due to intensity nonlinearity of the error-signal frequency shift. The experiment with $^{87}$Rb atoms in Ar-N$_2$ buffer gas atomic cell shows how the displacement value depends on different parameters. The possible influence of the effect on the clocks' frequency stability and reproducibility are discussed.
Dynamics of entropy and nonclassicality features of the interaction between a $\diamondsuit$-type four-level atom and a single-mode field in the presence of intensity-dependent coupling and Kerr nonlinearity
Ultrahigh free-electron Kerr nonlinearity in all-semiconductor waveguides for all-optical nonlinear modulation of mid-infrared light
Istituto Italiano di Tecnologia（意大利理工大学）；Center for Biomolecular Nanotechnologies（生物分子纳米技术中心）；Istituto di Fotonica e Nanotecnologie, Consiglio Nazionale delle Ricerche（国家研究委员会光子和纳米技术研究所）；Department of Physics, Sapienza University of Rome（罗马大学物理系）；Center for Life Nano- and Neuro-Science（生命纳米与神经科学中心）
