In an experiment, physicists from the University of Bonn and the University of Kaiserslautern-Landau observed and studied the properties of a one- to two-dimensional crossover in a gas of harmonically confined photons (light particles). The photons were confined in dye microcavities, while polymer nanostructures provided the trapping potential for the photon gas. By varying the aspect ratio of the trap, the researchers tuned it from an isotropic two-dimensional confinement to a highly elongated one-dimensional trapping potential. The team paper Published in a journal Natural Physics.
A polymer applied to the reflective surface confines the photonic gas within the light's parabola. The narrower this parabola is, the more one-dimensional the gas behaves. Image courtesy of University of Bonn.
“To create a gas from photons, you need to concentrate a lot of photons in a limited space and cool them at the same time,” said Dr Frank Wevinger from the University of Bonn.
In their experiments, Dr. Wewinger and his colleagues filled a small container with a dye solution and used a laser to excite it.
The resulting photons bounced back and forth between the reflective walls of the container.
Each time they collided with a dye molecule they cooled, eventually condensing the photon gas.
By modifying the reflective surface, we can affect the gas's dimensions.
“We were able to coat the reflective surface with a transparent polymer and create tiny microscopic protrusions,” said Dr Julian Schulz, a physicist at the University of Kaiserslautern-Landau.
“These protrusions allow us to confine and condense photons into one or two dimensions.”
“These polymers act as a kind of channel for the light,” said Dr Kirankumar Kalkihari Umesh, a physicist at the University of Bonn.
“The narrower this gap becomes, the more one-dimensional the gas behaves.”
In two dimensions, there is a precise temperature limit where condensation occurs, just as water freezes at exactly 0 degrees – physicists call this a phase transition.
“But if you create a one-dimensional gas instead of two-dimensional, things are a bit different,” Dr Wewinger said.
“So-called thermal fluctuations do occur in the photon gas, but in two dimensions they are so small that they have no practical effect.”
“But on one level, these fluctuations can make waves, figuratively speaking.”
These fluctuations destroy the order in a one-dimensional system, causing different regions in the gas to no longer behave in the same way.
As a result, phase transitions that are still precisely defined in two dimensions become increasingly blurred as the system becomes one-dimensional.
However, their properties are still governed by quantum physics, just like for two-dimensional gases, and these types of gases are called degenerate quantum gases.
It's as if water gets cold but doesn't freeze completely, but turns into ice at low temperatures.
“We were able to investigate this behavior for the first time in the transition from a two-dimensional to a one-dimensional photon gas,” Dr. Wewinger said.
The authors were able to demonstrate that a one-dimensional photon gas indeed does not have a precise condensation point.
By making small changes to the polymer structure, it becomes possible to study in detail what happens during the transition between different dimensions.
Although this is still considered fundamental research at this point, it has the potential to open up new applications of quantum optical effects.
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K. Kalkihari Umesh othersDimensional crossover in a quantum gas of light. National Physical SocietyPublished online September 6, 2024; doi: 10.1038/s41567-024-02641-7
Source: www.sci.news
