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Physicists observe a new phase of Bose-Einstein condensed light particles



Light particle abstract concept

A single “superphoton” composed of thousands of individual light particles: About ten years ago, researchers at the University of Bonn produced this extreme state of aggregation for the first time and proposed a new light source. This state is called the optical Bose-Einstein condensate, which has attracted many physicists since then because this exotic world of light particles is the home of its own physical phenomena.

Researchers led by Professor Martin Weitz, who discovered superphotons, and Professor Johann Kroha, a theoretical physicist, have returned to quantum from the latest “expedition”

; through a very special observation. world. They report a new, previously unknown phase transition in the Bose-Einstein optical condensate. This is the so-called over-damping phase. In the long run, the result may be related to encrypted quantum communication.The research has been published in the journal science.

Bose-Einstein condensate is an extreme physical state that usually occurs only at very low temperatures. Special feature: The particles in this system are no longer distinguishable, and are mainly in the same quantum mechanical state, in other words, they behave like a giant “superparticle”. Therefore, the state can be described by a single wave function.

In 2010, researchers led by Martin Weitz succeeded in producing Bose-Einstein condensate from light particles (photons) for the first time. Their special system is still in use today: physicists trap light particles in a resonator, which consists of two curved mirrors, the distance between the two mirrors is just over one micron, and they reflect fast Reciprocating light beams. This space is filled with a liquid dye solution, which can be used to cool the photons. This is done by the dye molecules “swallowing” photons and then ejecting them again, which brings the light particles to the temperature of the dye solution-equal to room temperature. Background: This system can first cool light particles because their natural characteristic is that they will dissolve when cooled.

Optical microresonator filled with dye solution

On the right is the microscope objective lens, which is used to observe and analyze the light emitted from the resonator. Image source: ©GregorHübl/ Uni Bonn

Clear separation of the two phases

The phase transition is what physicists call the transition between water and ice during freezing. But how does a specific phase change occur within the trapped light particle system? Scientists explain it this way: a semi-transparent mirror will cause photons to be lost and replaced, causing an imbalance, causing the system to be unable to assume a certain temperature and enter an oscillation state. This creates a transition between the oscillating phase and the damping phase. Damping means that the amplitude of vibration is reduced.

Fahri Emre Öztürk, a doctoral student at the Institute of Applied Physics at the University of Bonn, said: “It can be said that the over-damping phase we observe corresponds to a new state of the light field.” Special The characteristic is that the effect of the laser is usually not separated from the effect of the Bose-Einstein condensate through a phase change, and there is no clearly defined boundary between the two states. This means that physicists can constantly move back and forth between effects.

Martin Weitz

Optical setup on the measuring table of the Institute of Applied Physics of the University of Bonn. Image source: ©GregorHübl/ Uni Bonn

“However, in our experiment, the over-damped state of the optical Bose-Einstein condensate was separated by oscillation and the phase change of the standard laser,” said research leader Professor Martin Weitz. “This shows that there is a Bose-Einstein condensate whose state is indeed different from that of a standard laser. He emphasized: “In other words, we are dealing with two separate stages of the optical Bose-Einstein condensate. . “

The researchers plan to use their findings as the basis for further research to find new states of the light field in a variety of coupled photocondensates, which may also occur in the system. Fahri Emre Öztürk said: “If a suitable quantum mechanical entanglement appears in the coupled light condensate, this may be interesting for the transmission of quantum encrypted messages between multiple participants.”

New status research team

Dr. Martin Weitz, Dr. Julian Schmitt, Dr. Frank Vewinger, Dr. Johann Kroha and Prof. Göran Hellmann from the Institute of Applied Physics at the University of Bonn. Image source: ©GregorHübl/ Uni Bonn

Reference: “Observation photons gas phase transition in non-Hermitian” OF: Fahri EmreÖztürk, Tim Lappe, GöranHellmann, Julian Schmitt, Jan Klaers, Frank Vewinger, Johann Kroha and Martin Weitz, 2021 years. 4 2 April, science.
DOI: 10.1126/science.abe9869

The research was supported by the cooperative research center TR 185 “OSCAR-through tailor-made atomic and photon quantum matter coupling to the reservoir” of the University of Kaiserslautern and the University of Bonn, as well as from the universities of Cologne, Aachen, Bonn and Cologne. Funding of Excellence Cluster ML4Q. Jülich, a research center funded by the German Research Foundation. The cluster of excellence is embedded in the interdisciplinary research field (TRA) of the University of Bonn, “the basis for the interaction of matter and foundation”. In addition, this research was funded by the European Union under the “PhoQuS-Quantum Simulation Photonics” project and the German Aerospace Center, funded by the Federal Ministry of Economics and Energy.




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