Quantum leap: Scientists make light waves "stand still"

Scientists have discovered a novel method to manipulate light waves by deforming the two-dimensional photonic crystal that contains them. This discovery opens up new possibilities for the development of nanophotonic chips and has the potential to revolutionize the field of photonics, spawning new lasers and quantum devices.

Controlling light waves with photonic crystals

A team of researchers from AMOLF, in collaboration with Delft University of Technology, has successfully brought light waves to a halt by deforming the two-dimensional photonic crystal that contains them.

The researchers demonstrate that even a subtle deformation can have a substantial effect on photons in the crystal, resembling the effect that a magnetic field has on electrons.

“This principle offers a new approach to slow down light fields and thereby enhance their strength. Realizing this on a chip is particularly important for many applications,” says AMOLF-group leader Ewold Verhagen.

Inspiration and lessons learned from electrons

The researchers drew inspiration from the way electrons behave in materials. In a conductor, electrons can move freely, but an external magnetic field can stop this motion.

The circular movement caused by the magnetic field stops conduction, and electrons can only exist in the material if they have very specific energies, known as Landau levels.

In graphene, a two-dimensional material consisting of a single layer of carbon atoms arranged in a crystal, Landau levels can also be caused by a different mechanism than a magnetic field.

When the crystal array is deformed, such as by stretching it like elastics, conduction is stopped, and the material turns into an insulator, binding the electrons to Landau levels.

Applying the concept to photons

The group of Verhagen, in collaboration with Kobus Kuipers of Delft University of Technology, demonstrated a similar effect for light in a photonic crystal.

“A photonic crystal normally consists of a regular — two dimensional — pattern of holes in a silicon layer. Light can move freely in this material, just like electrons in graphene,” says first author René Barczyk, who successfully defended his Ph.D. thesis on this topic in 2023.

“Breaking this regularity in exactly the right manner will deform the array and consequently lock the photons. This is how we create Landau levels for photons,” Barczyk concluded.

In Landau levels, light waves no longer move; they stand still instead of flowing through the crystal. The researchers succeeded in demonstrating this, showing that the deformation of the crystal array has a similar effect on photons as a magnetic field on electrons.

Steering light waves on a chip with deformation patterns

Verhagen says, “By playing with the deformation pattern, we even managed to establish various types of effective magnetic fields in one material. As a result, photons can move through certain parts of the material but not in others. Hence, these insights also provide new ways to steer light on a chip.”

Simultaneously, a research team from Pennsylvania State University has published an article in the same journal about how they demonstrated — independently from the Dutch team — an identical effect.

While some details in the approach differed, both teams were able to stop light waves from moving and observe Landau levels by deforming a two-dimensional photonic crystal.

“This brings on-chip applications closer. If we can confine light at the nanoscale and bring it to a halt like this, its strength will be enhanced tremendously,” Verhagen explained.

“And not only at one location, but over the entire crystal surface. Such light concentration is very important in nanophotonic devices, for example for the development of efficient lasers or quantum light sources,” he concluded.

Controlling light waves spawns a new era in nanophotonics

The discovery of harnessing the power of deformation to control light waves marks a significant milestone in the field of nanophotonics.

By manipulating photonic crystals through subtle deformations, researchers have unlocked a new era of possibilities for on-chip applications, light concentration, and the development of efficient lasers and quantum light sources.

This breakthrough, independently confirmed by two research teams, paves the way for unprecedented control over light at the nanoscale, promising to revolutionize the future of photonics and open up exciting avenues for technological advancement.

The full study was published in the journal Nature Photonics.

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