💥 Quantum effects of the early Universe reproduced in the lab

In quantum physics, a vacuum is not completely empty. It is constantly traversed by minuscule fluctuations, like very faint vibrations. These movements usually remain invisible. But under certain conditions, they can be amplified and give rise... to particles.

This mechanism, called parametric amplification, can be compared to a simple phenomenon. It is like a swing to which regular pushes are applied at the right moment. The movement amplifies progressively. Here, it's the vacuum fluctuations that are "pushed" until they become observable.


To test this idea, scientists used a gas of helium atoms cooled to an extremely low temperature, close to absolute zero. At this level of cold, matter adopts very particular behavior, governed by quantum laws.

The gas is held in place using laser beams. By varying the intensity of one of these lasers in a regular manner, the researchers provoke a controlled vibration of the system. This oscillation acts like the pushes on the swing and amplifies certain fluctuations.

Result: excitations appear in the gas. They are called phonons, which can be seen as small "waves" of energy propagating through the medium, and are akin to "quasi-particles." But one difficulty remains: some of these excitations can also come from the residual temperature of the gas, even if it is very low.

To ensure they indeed originate from the quantum vacuum, the researchers looked for a specific signature. They showed that these phonons appear in closely linked pairs, in a phenomenon of quantum entanglement. This means their properties are strongly correlated, in a way impossible to explain with classical physics.

This observation is important because it confirms that vacuum fluctuations indeed served as the starting point. Until now, this entanglement had been predicted by theory but never directly observed in this type of system.

Beyond this demonstration, the experiment opens new perspectives. By increasing the number of these excitations, researchers will be able to study how they interact with each other. This collective behavior remains difficult to describe with current theoretical tools.

This work also interests cosmologists. Indeed, similar mechanisms could have occurred just after the Big Bang, when the Universe was rapidly expanding and particles appeared from initial fluctuations.

This type of experiment therefore acts as a miniature model of the cosmos. By recreating these conditions in the laboratory, scientists have a valuable tool to better understand phenomena that occurred at the origin of our Universe.

This advance is described in the journal Physical Review Letters.