Conservation of the spin and orbital angular momenta in electromagnetism

By K. Bliokh, Justin Dressel, Franco Nori. 2014

166 citations recorded by the source corpus.

We review and re-examine the description and separation of the spin and orbital angular momenta (AM) of an electromagnetic field in free space. While the spin and orbital AM of light are not separately meaningful physical quantities in orthodox quantum mechanics or classical field theory, these quantities are routinely measured and used for applications in optics. A meaningful quantum description of the spin and orbital AM of light was recently provided by several authors, which describes separately conserved and measurable integral values of these quantities. However, the electromagnetic field theory still lacks corresponding locally conserved spin and orbital AM currents. In this paper, we construct these missing spin and orbital AM densities and fluxes that satisfy the proper continuity equations. We show that these are physically measurable and conserved quantities. These are, however, not Lorentz-covariant, so only make sense in the single laboratory reference frame of the measurement probe. The fluxes we derive improve the canonical (nonconserved) spin and orbital AM fluxes, and include a ‘spin–orbit’ term that describes the spin–orbit interaction effects observed in nonparaxial optical fields. We also consider both standard and dual-symmetric versions of the electromagnetic field theory. Applying the general theory to nonparaxial optical vortex beams validates our results and allows us to discriminate between earlier approaches to the problem. Our treatment yields the complete and consistent description of the spin and orbital AM of free Maxwell fields in both quantum-mechanical and field-theory approaches.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/27658bf136f39a6a6f9df9eaaa1d87e65a5c65f7

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In Artificial Intelligence

1. Franco Nori
2. K. Bliokh
3. A. Bekshaev
4. Sahel Ashhab
5. I. Georgescu
6. J. You

In Atomic and Molecular Physics, and Optics

1. Franco Nori
2. K. Bliokh
3. A. Bekshaev
4. I. Mokhun
5. Zheng Jun
6. C. Zenkova
7. S. Hanson
8. O. Angelsky

Citations in the corpus

• Transverse and longitudinal angular momenta of light (2015, background): “L ∝  E2 − H2  [34,37], while the dual-symmetric definitions (2.”
• Structured Light: Ideas and Concepts (2020, background): “In addition, to finalize the recital of DCs, we mention the electromagnetic helicity [60, 66], which is especially important for various aspects of the chiral interactions and electromagnetic duality manifestations in structured light fields:”