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Physicists ‘trick’ photons into behaving like electrons using a ‘synthetic’ magnetic field


Effort on a honeycomb metasurface generates an artificial magnetic field for light, which can be adjusted by embedding the meta surface in a cavity waveguide. Credit: University of Exeter

Scientists have discovered an elegant way to manipulate light using a ̵

6;synthetic’ Lorentz force – which in nature is responsible for many fascinating phenomena, including the Aurora Borealis.

A team of theoretical physicists from the University of Exeter have been pioneering a new technique for creating tunable artificial magnetic fields that allow photons to mimic the dynamics of charged particles in true magnetic fields.

The team believes in the new research published in leading journal Nature photonics, could have important implications for future photonic devices, as it provides a new way of manipulating light below the diffraction limit.

When charged particles, such as electrons, pass through a magnetic field, they feel a Lorentz force due to their electric charge, which curves their orbit around the magnetic field lines.

This Lorentz force is responsible for many fascinating phenomena ranging from the beautiful Northern Lights to the famous Quantum-Hall effect, the discovery of which was awarded the Nobel Prize.

However, because photons do not carry an electric charge, they cannot be directly controlled using true magnetic fields, as they do not experience a Lorentz force; a severe limitation dictated by the fundamental laws of physics.

The research team has shown that it is possible to create artificial magnetic fields for light by distorting honeycomb metasurface surfaces – ultra-thin 2-D surfaces that are designed to have structure on a scale that is much smaller than the wavelength of light.

The Exeter team was inspired by a remarkable discovery ten years ago in which it was shown that electrons propagating through a strained graphene membrane behave as if they were exposed to a large magnetic field.

The main disadvantage of this stress engineering approach is that in order to set the artificial magnetic field, it is necessary to change the stem pattern with precision, which is extremely challenging, if not impossible, to do with photonic structures.

Exeter physicists have proposed an elegant solution to overcome this fundamental lack of voting.

Charlie-Ray Mann, the lead scientist and author of the study, explains: “These metasurfaces support hybrid light material excitations, called polaritons, which are trapped on the meta-surface.

“They are then deflected by the distortions in the meta-surface in the same way as magnetic fields deflect charged particles.

“By taking advantage of the hybrid character of the polaritons, we show that you can set the artificial magnetic field by changing the real electromagnetic environment surrounding the meta surface.”

For the study, the researchers embedded the meta-surface between two mirrors – known as a photonic cavity – and show that one can adjust the artificial magnetic field by only changing the width of the photonic cavity, thereby eliminating the need to change the distortion in the meta-surface.

Charlie added: “We have even demonstrated that you can completely turn off the artificial magnetic field in a critical cavity width without having to remove the distortion in the meta surface, something that is impossible to do in the graph or any system that mimics the graph.

Using this mechanism, you can bend the orbit of the polariton using an adjustable Lorentz-like force and also observe Landau quantization of the polariton-cyclotron orbits in direct analogy with what happens to charged particles in true magnetic fields.

“Furthermore, we have shown that you can drastically reconfigure the polariton Landau level spectrum by simply changing the cavity width.”

Dr. Eros Mariani, the lead supervisor of the study, said: “Being able to mimic phenomena with photons that are normally thought to be exclusive to charged particles is fascinating from a basic point of view, but it can also have important consequences for photonics. applications.

“We are excited to see where this discovery leads as it poses many intriguing questions that can be explored on many different experimental platforms across the electromagnetic spectrum.”

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More information:
Mann, C., Horsley, SAR & Mariani, E. Tunable pseudo-magnetic fields for polaritons in strained metasurfaces. Night. Photonics (2020). doi.org/10.1038/s41566-020-0688-8, www.nature.com/articles/s41566-020-0688-8

Provided by the University of Exeter

Citation: Physicists’ trick photons into behaving like electrons using a ‘synthetic’ magnetic field (2020, 14 September) retrieved 14 September 2020 from https://phys.org/news2020-09-physicists-photons-electrons- synthetic- magnetic.html

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