Natural line shape

TL;DR

This paper analyzes how the spectral line shape of spontaneous emission varies with different excitation procedures, revealing dependence on pulse form and implications for quantum Zeno effect and quantum jump duration.

Contribution

It provides a detailed calculation of the emission spectrum for a two-level atom excited by a pi pulse, highlighting the influence of pulse shape on spectral features.

Findings

Central spectral part is Lorentzian.

Spectral wings decay faster beyond Rabi frequency detuning.

Pulse shape affects the spectral line wings.

Abstract

The observable line shape of the spontaneous emission depends on the procedure of atom's excitation. The spectrum of radiation emitted by a two-level atom excited from the ground state by a pi pulse of the resonant pump field is calculated for the case when the Rabi frequency is much larger than the relaxation rate. It is shown that the central part of the spectral distribution has a standard Lorentzian form, whereas for detunings from the resonance that are larger than the Rabi frequency the spectral density falls off faster. The shape of the wings of the spectral line is sensitive to the form of the pi pulse. The implications for the quantum Zeno effect theory and for the estimates of the duration of quantum jumps are discussed.