More surprises in Optical Momentum…

Electromagnetic momentum is a topic with rich history dating back to Maxwell, Poynting, Minkowski, Abraham, Einstein, and many more1.
It has also led to new questions, and an intriguing controversy in electromagnetism2.

An interesting and contemporary question to ask is: what is the behavior of optical momentum in artificial materials ?

One class of artificial materials is the near zero-refractive index (NZI) materials.

What are NZI materials ? The general definition of refractive index from a material view point is that it is proportional to square root of a product: dielectric permittivity (ε) and magnetic permeability (μ) of the given material.

n = (εμ)½ 

 If either of these material values go to zero at a given wavelength of light, then the refractive index goes to zero or close to zero. Such a situation creates new opportunity for enhanced or supressed light-matter interaction. See this popular review on NZI materials3

A recent theoretical paper4 addresses the consequence of evolution of optical momentum in NZI media.
This analysis has thrown a few fundamental surprises that are fascinating such as : absence of interference in Young’s double slit experiments, and some new opportunities in optical cloaking thanks to quantum nature of light. To quote the authors4 :

being inside an NZI materials would lead to an infinite uncertainty on position and zero uncertainty on momentum. Conceptually, this implies that since the resolution is poor and no correct image can be formed, an object of any shape and material can be “hidden” in a NZI material.

There are a few more interesting prospects, and of course, all of them are yet to be verified with experiments.

If you are interested in this topic, I strongly recommend this recent, popular level article5

1.           M. Buchanan, “Minkowski, Abraham and the photon momentum,” 2, Nature Phys 3(2), 73–73, Nature Publishing Group (2007) [doi:10.1038/nphys519].

2.           S. M. Barnett and R. Loudon, “The enigma of optical momentum in a medium,” Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 368(1914), 927–939, Royal Society (2010) [doi:10.1098/rsta.2009.0207].

3.           “Optics & Photonics News – Zero-Index Platforms: Where Light Defies Geometry,” <> (accessed 5 May 2022).

4.           M. Lobet et al., “Momentum considerations inside near-zero index materials,” 1, Light Sci Appl 11(1), 110, Nature Publishing Group (2022) [doi:10.1038/s41377-022-00790-z].

5.           “Exotic Materials Through Momentum’s Looking-Glass,” <> (accessed 5 May 2022).

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