In a groundbreaking feat, physicists have successfully created a one-dimensional gas composed entirely of light, marking the first time such a feat has been accomplished. This new state of matter, aptly named a photon gas, could revolutionize our understanding of how photons, or particles of light, behave at the quantum level.
The team of researchers achieved this remarkable breakthrough by firing a laser into a reflective container filled with dye. This process caused the photons within the laser beam to cool down and ultimately condense, leading to the formation of the photon gas. Their findings were published on September 6th in the prestigious journal Nature Physics.
“To create these types of gases, we need to concentrate lots of photons in a confined space and cool them simultaneously,” explained study senior author Frank Vewinger, a physicist at the University of Bonn, in a statement.
Photons, being bosons, possess an interesting characteristic known as integer spin. This means that they can occupy the same state and space concurrently. When a gas of bosons is cooled to near absolute zero, all its particles lose their energy, entering the same energy states.
Since we can only differentiate between these otherwise identical particles in a gas cloud by observing their energy levels, this equalizing effect has profound implications. What was once a disparate cloud of vibrating, jiggling, and colliding particles in a warmer gas transforms, from a quantum mechanical perspective, into perfectly identical particles. This process gives rise to an elusive form of matter known as a Bose-Einstein condensate.
The existence of a condensate form leads to a fascinating phenomenon: the particles’ positions within the gas become highly uncertain. Consequently, the potential locations that each particle could occupy expand to encompass a larger area than the spaces between the particles themselves. As a result, instead of being discrete objects, the overlapping photons in a photon gas behave as if they were a single, giant particle.
While physicists have successfully created photon gases in two dimensions before, generating a one-dimensional photon gas presented a significantly greater challenge. “Things are a little different when we create a one-dimensional gas instead of a two-dimensional one,” stated Vewinger. “So-called thermal fluctuations take place in photon gases, but they are so small in two dimensions that they have no real impact. However, in one dimension, these fluctuations can — figuratively speaking — make big waves.”
To overcome this hurdle, the researchers filled a minuscule, reflective container with a dye solution and then fired a laser into it. The laser photons bounced back and forth within the container until they collided with the dye molecules, losing energy in the process and clustering together.
The researchers then ingeniously applied a transparent polymer to the container’s reflective walls. This manipulation enabled them to fine-tune the way light was reflected, effectively condensing it in one dimension, essentially creating a line of light. “These polymers act like a type of gutter, but in this case for light,” explained lead author Kirankumar Karkihalli Umesh, a doctoral student at the University of Bonn. “The narrower this gutter is, the more one-dimensionally the gas behaves.”
By closely studying their newly created one-dimensional photon gas, the researchers confirmed that it exhibited distinct behavior compared to its two-dimensional counterpart. Unlike the two-dimensional photon gases, the thermal fluctuations in the one-dimensional version prevented complete condensation in certain regions. This resulted in a partial phase transition between laser light and its condensate form, which was “smeared out” across the gas. It’s analogous to icy water that hasn’t fully frozen.
This groundbreaking research paves the way for a deeper understanding of the quantum world and its potential applications. The researchers believe that investigating the differences in behavior across dimensions could lead to the discovery of novel quantum optical effects. The future of quantum optics seems brighter than ever before, thanks to this remarkable achievement.
