Extremely cold atoms can control the shape and direction of light when they work together, relying on a type of physics proposed more than 400 years ago but only now proven to be possible.

To manipulate both the electrical and magnetic interactions between atoms and light, previous work had to rely on specially designed meta-materials.

But Janne Ruostekoski at Lancaster University in the UK, and his colleagues have now shown this can be done with naturally occurring elements, such as ytterbium or strontium. They calculated that manipulating the behaviour of atoms cooled to a billionth of a degree Kelvin above absolute zero makes them into a powerful instrument for shaping light.

At these temperatures, the atoms move extremely slowly and can be controlled through quantum mechanical effects that are negligible at higher temperatures.

The team used lasers to excite the atoms and coax them into one shared motion. They found that when the atoms act collectively, they can shape and steer light through their electrical and magnetic interactions with it. The shared behavior allows them to act like a collection of electric charges or very small magnets that affect the light.

Harnessing magnetic interactions in particular is a new and important aspect of this work, says David Wilkowski at the National University of Singapore, who was not involved with the study.

This research also connects to the 17th century theories of the physicist Christiaan Huygens. Ruostekoski’s team effectively found a way to build a so-called Huygens’ surface out of ultracold atoms.

Each point – each atom – on this surface determines the shape of the emanating wave of light that passes through it, which makes it a tool for engineering light waves that have any wanted attributes. This work could help us study quantum information and potentially improve quantum memory devices by using the cooperative atom-light interaction.

Reference: arxiv.org/abs/2002.12930