EIT-related phenomena and their mechanical analogs

TL;DR

This paper reviews classical harmonic oscillator models for electromagnetically induced transparency (EIT), establishing a one-to-one correspondence with quantum systems, and validates these analogs through experimental data, providing new insights into EIT phenomena.

Contribution

It introduces a novel mechanical analog for EIT systems, demonstrating a direct correspondence between classical oscillators and quantum EIT configurations, validated by experimental results.

Findings

Classical harmonic oscillators can model atomic EIT transitions.

The mechanical analog accurately reproduces EIT dark states.

Experimental data supports the classical-quantum correspondence.

Abstract

Systems of interacting classical harmonic oscillators have received considerable attention in the last years as analog models for describing electromagnetically induced transparency (EIT) and associated phenomena. We review these models and investigate their validity for a variety of physical systems using two- and three-coupled harmonic oscillators. From the simplest EIT-$\Lambda$ configuration and two-coupled single cavity modes we show that each atomic dipole-allowed transition and a single cavity mode can be represented by a damped harmonic oscillator. Thus, we have established a one-to-one correspondence between the classical and quantum dynamical variables. We show the limiting conditions and the equivalent for the EIT dark state in the mechanical system. This correspondence is extended to other systems that present EIT-related phenomena. Examples of such systems are two- and three-level (cavity EIT) atoms interacting with a single mode of an optical cavity, and four-level atoms in a inverted-Y and tripod configurations. The established equivalence between the mechanical and the cavity EIT systems, presented here for the first time, has been corroborated by experimental data. The analysis of the probe response of all these systems also brings to light a physical interpretation for the expectation value of the photon annihilation operator $\left\langle a\right\rangle$. We show it can be directly related to the electric susceptibility of systems, the composition of which includes a driven cavity field mode.