Time-dependent spectra of quantum beats

TL;DR

This paper investigates the time-dependent spectra of quantum beats in a multilevel emitter, revealing how interference affects spectral features over time in spontaneous emission and resonance fluorescence.

Contribution

It introduces a detailed analysis of time-resolved spectra showing the evolution of quantum beats and highlights the importance of filter bandwidth in spectral resolution.

Findings

Spontaneous emission spectrum transitions from a broad peak to a doublet and fades over time.

Resonance fluorescence exhibits doublet sidebands that grow asymmetrically then symmetrize.

Filter bandwidth critically influences spectral resolution and observed dynamics.

Abstract

We obtain time-resolved spectra of spontaneous emission and resonance fluorescence of a single multilevel emitter where two antiparallel transitions interfere and cause quantum beats. After rising as a single broad peak, the spontaneous emission spectrum turns into a doublet of subnatural peaks and then fades for long times. For strong field resonance fluorescence, the beat signature is the formation of doublet sidebands, which initially grow asymmetrically but end up symmetrical. We stress the filter bandwidth's crucial role in the spectral resolution and causal evolution.