Quantum interference in the resonance fluorescence of a $J=1/2$-$J'=1/2$ atomic system: Quantum beats, nonclassicality, and non-Gaussianity

TL;DR

This paper theoretically investigates quantum interference effects in the resonance fluorescence of a $J=1/2$-$J'=1/2$ atomic system, revealing quantum beats, nonclassicality, and non-Gaussianity influenced by magnetic fields and laser parameters.

Contribution

It introduces a detailed analysis of quantum beats and nonclassical properties in a specific atomic system with interference effects, expanding understanding of quantum fluorescence phenomena.

Findings

Quantum beats occur at frequencies related to Rabi frequencies and Zeeman splitting.

Fluorescence exhibits nonclassical and non-Gaussian features, especially in the beat regime.

Cross terms in correlations are less significant than interference effects in the system.

Abstract

We study theoretically quantum statistical and spectral properties of the resonance fluorescence of a single atom or system with angular momentum $J=1/2 - J'=1/2$ driven by a monochromatic linearly polarized laser field, due to quantum interference among its two antiparallel, $\pi$ transitions. A magnetic field parallel to the laser polarization is applied to break the degeneracy (Zeeman effect). In the nondegenerate case, the $\pi$ transitions evolve at different generalized Rabi frequencies, producing quantum beats in the intensity and the dipole-dipole, intensity-intensity, and quadrature-intensity correlations. For a strong laser and large Zeeman splitting the beats have mean and modulation frequencies given by the average and difference, respectively, of the Rabi frequencies, unlike thebeats studied in many spectroscopic systems, characterized by a modulated exponential-like decay. Further, the Rabi frequencies are those of the pairs of sidebands of the Mollow-like spectrum of the system. In the two-time correlations, the cross contributions, i.e., those with products of probability amplitudes of the two $\pi$ transitions, have a lesser role than those from the interference of the probability densities. In contrast, there are no cross terms in the total intensity. We also consider nonclassical and non-Gaussian properties of the phase-dependent fluorescence for the cases of weak to moderate excitation and in the regime of beats. The fluorescence in the beats regime is nonclassical, mainly from third-order dipole fluctuations, which reveal them to be also strongly non-Gaussian, and their quadrature spectra show complex features around the Rabi frequencies. For small laser and Zeeman detunings, a weak to moderate laser field pumps the system partially to one of the ground states, showing slow decay in the two time correlations and a narrow peak in the quadrature spectra.