Observability of the superkick effect within a quantum-field-theoretical approach

TL;DR

This paper investigates the superkick effect, where an atom in an optical vortex gains unexpectedly large transverse momentum upon photon absorption, using a quantum field theoretical approach to clarify and extend previous classical wave packet analyses.

Contribution

It provides the first quantum field theoretical analysis of the superkick effect, confirming its observability and exploring its limits when the beam focus size approaches the beam's offset distance.

Findings

Superkick effect confirmed within QFT framework

Limits of the effect identified when focusing size approaches beam offset

Resolved paradoxes related to the QFT formalism

Abstract

An atom placed in an optical vortex close to the axis may, upon absorbing a photon, acquire a transverse momentum much larger than the transverse momentum of any plane-wave component of the vortex lightfield. This surprising phenomenon dubbed superkick has been clarified previously in terms of the atom wave packet evolution in the field of an optical vortex treated classically. Here, we study this effect within the quantum field theoretical (QFT) framework. We consider collision of a Bessel twisted wave with a compact Gaussian beam focused to a small focal spot $\sigma$ located at distance $b$ from the twisted beam axis. Through a qualitative discussion supported by exact analytical and numerical calculations, we recover the superkick phenomenon for $\sigma \ll b$ and explore its limits when $\sigma$ becomes comparable to $b$. On the way to the final result within the QFT treatment, we encountered and resolved apparent paradoxes related to subtle issues of the formalism. These results open a way to a detailed QFT exploration of other superkick-related effects recently suggested to exist in high-energy collisions.