# Comment on half-integer quantum numbers for the total angular momentum of photons in light beams with finite lateral extensions

## TL;DR

This paper critically examines recent claims that photons in finite light beams can have half-integer total angular momentum, contrasting quantum and classical results and clarifying misconceptions about angular momentum transfer.

## Contribution

It provides a critical analysis showing that classical magnetic moment results do not support the quantum claim of half-integer angular momentum for photons in finite beams.

## Key findings

- Quantum result of half-integer angular momentum is not supported by classical magnetic moment calculations.
- Classical calculations show the magnetic moment is smaller than expected if angular momentum transfer were as claimed.
- No evidence suggests the classical magnetic moment reflects the quantum angular momentum transfer.

## Abstract

Recently the spectacular result was derived quantum mechanically that the total angular momentum of photons in light beams with finite lateral extensions can have half-integer quantum numbers. In a circularly polarized Gauss light beam it is half of the spin angular momentum which it would have in a respective infinitely extended wave. In another paper it was shown by a classical calculation that the magnetic moment induced by such a beam in a metal is a factor of two smaller than the one induced by a respective infinitely extended wave. Since the system's angular momentum is proportional to its magnetic moment it could be assumed that the classical result for the magnetic moment reflects the transfer of the total angular momenta of the beam photons to the metal. Here we show that there is no hint that this is indeed the case.