Observability of the superkick effect within a quantum-field-theoretical approach
Igor Ivanov, Bei Liu, Pengming Zhang
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 light field. 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 $\ensuremath{\sigma}$ 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 $\ensuremath{\sigma}\ensuremath{\ll}b$ and explore its limits when $\ensuremath{\sigma}$ 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.