Quantum "ping-pong" game played by two atoms controlling photons

Light is a fundamental aspect of our daily lives, often taken for granted. It’s well-known that atoms can absorb and reemit light, now scientists have coerced two atoms into engaging in game of quantum ping pong.

Controlling atoms and how they emit and absorb light, as seen in this simulation, has always been a challenge due to the random nature of light emission.

However, a discovery by a research team at TU Wien in Vienna, Austria, is set to change this narrative.

Harnessing light: Breakthrough in photon control

The team, led by Prof. Stefan Rotter and first author Oliver Diekmann, has theorized a method that guarantees a photon emitted by one atom is reabsorbed by another.

This innovative approach involves a special lens, inspired by the unique properties of the fish-eye lens developed by James Clerk Maxwell.

“If an atom emits a photon somewhere in free space, the direction of emission is completely random. This makes it practically impossible to get another distant atom to catch this photon again,” says Prof. Stefan Rotter from the Institute of Theoretical Physics at TU Wien.

“The photon propagates as a wave, which means that nobody can say exactly in which direction it is travelling. It is therefore pure chance whether the light particle is reabsorbed by a second atom or not.”

Drawing inspiration from acoustics

The team’s solution draws an analogy from acoustics, specifically the phenomenon observed in whispering galleries.

In such galleries, people can hear each other across distances by whispering, thanks to the elliptical shape of the room focusing sound waves.

“In principle, something similar could be built for light waves when positioning two atoms at the focal points of an ellipse,” says Oliver Diekmann, the first author of the current publication.

“But in practice, the two atoms would have to be positioned very precisely at these focal points.”

Similarly, the researchers propose positioning two atoms at the focal points of an elliptical environment to control the trajectory of light.

Maxwell fish-eye lens and quantum ping pong

However, the precision required for positioning the atoms in an elliptical setup is impractical. This is where the concept of the Maxwell fish-eye lens comes into play.

This lens, with its spatially varying refractive index, bends the light rays, ensuring that photons from one atom follow a curved path to the target atom.

“In this way, it is possible to ensure that all rays emanating from one atom reach the lens’s edge on a curved path, are subsequently reflected and then arrive at the target atom on another curved path,” explains Oliver Diekmann.

How to play quantum ping pong

In this case, the effect works much more efficiently than in a simple ellipse and deviations from the ideal positions of the atoms are less harmful.

This method is better than the simple elliptical approach, and less sensitive to deviations in the atoms’ positioning.

It represents a significant leap in controlling light-matter interactions, with the photon passing between atoms like in a game of quantum ping-pong, where each atom alternately plays the role of sender and receiver.

After absorbing the photon, the atom enters a state of higher energy and quickly reemits the photon.

Then, the process restarts. The two atoms exchange roles, and the receiver atom sends the photon back to the original sender atom – continuing this cycle.

Practical applications and the future

The practical applications of this theory are vast. “Theoretically, we’ve demonstrated the effect, and it’s feasible with today’s technology,” adds Prof. Rotter.

“In practice, using groups of atoms instead of individual ones could further enhance efficiency. This concept opens up new avenues for quantum control systems and studying strong light-matter interactions.”

In summary, the TU Wien team’s work marks a pivotal moment in photon control.

Their approach, blending theoretical physics and optical engineering, is a huge advancement for quantum computing and communication, showcasing the incredible potential of light manipulation.

The full study was published in the journal Physical Review Letters.

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