# How many atoms get excited when they decay?

## TL;DR

This paper explores how to control and herald the excitation of a two-level quantum emitter during decay by manipulating detection methods, providing insights into quantum state preparation and emission dynamics.

## Contribution

It introduces a method to steer the evolution of a two-level system and herald its full excitation during decay through specific detection strategies.

## Key findings

- Heralded preparation of fully excited states during decay
- Control over emitter evolution via detection choices
- Quantitative probability of excitation during decay

## Abstract

We analyze the time evolution of a two-level system prepared in a superposition of its ground state and radiatively unstable excited state. We show that by choosing appropriate means of detection of the radiated field, we can steer the evolution of the emitter and herald its preparation in the fully excited state. We determine the probability for the occurrence of this "excitation during the decay" of a remote emitter.