Radiative friction on an excited atom moving in vacuum

TL;DR

This paper investigates how an excited atom moving in vacuum experiences a friction force due to spontaneous emission, resulting from entanglement and momentum transfer, with implications for atomic motion in quantum electrodynamics.

Contribution

It provides a detailed analysis of the friction force on an excited atom in vacuum, highlighting the quantum effects of entanglement and photon recoil on atomic dynamics.

Findings

The atom experiences a friction force opposite to its initial velocity.

The force arises from entanglement and momentum transfer during spontaneous emission.

Properties of the friction force are characterized and discussed.

Abstract

It is known that, when an excited atom spontaneously emits one photon, two effects are produced. First, the atom's internal and external states are entangled with the states of the emitted photon. Second, the atom receives a momentum transfered from the photon. In this work, the dynamics of such an atom in vacuum is studied. Through a specific calculation, it is demonstrated that these effects cause the atom to experience, on average, a friction force opposite to its initial velocity. Properties of the force are also discussed.