First experimental boson stimulation of atomic light scattering in a very cold gas

When the photon scatters, the photon’s recoil changes the momentum of the atom by q (red arrow). a, Above the phase transition (T > TC), both the initial and final momentum states are in the thermochromic cloud. b, under the transition stage (T

Bosons, one of two basic classes of particles, have been the focus of countless physics studies. When a boson particle transitions into an already occupied final quantum state, the rate of this transition is enhanced by what is called a “occupation number” , an effect known as bosonic stimulation. The appearance of bosonic stimulation in light scattering processes was first predicted more than three decades ago, yet observing it directly in experimental settings has so far proved difficult.

Researchers at the MIT-Harvard Center for Ultracold Atoms recently observed enhanced bosonic light scattering in an ultracold gas for the first time. Their findings, published in nature physicscould open exciting new possibilities for the study of bosonic systems.

Yu-Kun Lu, one of the researchers who conducted the study, told “For bosons, the rate of transition to an already occupied quantum state is boosted by its occupation number: the boson stimulus effect”.

“While bosonic stimulation has been observed in various forms, bosonic stimulation of light scattering was predicted more than 30 years ago but has proven elusive for direct observation. In simple terms, if one turbulently illuminated a Bose ideal gas and observed an enhancement of light scattering when approaching quantum decay, that would be evidence “smoke cannon” on bosonic improvement “.

For their experiment, Lu and his colleagues prepared an extremely cold cloud of 23Na gas has a high density. Then they shined a light on it and measured the number of scattered photons emerging from the system.

They found that the scattering of the photons was indeed enhanced before the system moved into the Bose-Einstein condenser (BEC). However, this enhancement becomes larger even below the point of the phase transition, which is what theory predicts would happen in the presence of the bosonic stimulus.

Lu explained: “We noticed an improvement of light scattering already above the BEC phase transition and a more pronounced improvement without the phase transition”. “By comparing the data with the theoretical prediction, we discovered that the interaction between atoms can also affect light scattering, especially under phase transition. Furthermore, we showed that for a multilevel system prepared in a single internal state, the bosonic enhancement occurs only for Rayleigh scattering but not for Raman scattering. “.

The latest study by Lu and colleagues presents the first experiment of bosonic stimulation of the scattering of atom light in an extremely cold gas. The team’s observations clearly illustrate how quantum statistics and interactions can modify the optical properties of Bose’s gas.

Lu added: “Understanding the interaction between quantum statistics, interaction, and phase transition in light scattering processes is not only of fundamental importance, but is also important for the quantitative diagnosis of bosonic systems using optical methods.”. “In our future work, it would be promising to study the bosonic enhancement of light scattering in a potential box due to intensity inhomogeneities. In this case, the effect of reinforcement will be larger, and the study of the interaction effect will be more explicit “.

In their next studies, the researchers also hope to use light scattering to characterize highly interacting systems, including those with strong dipole interactions, that are anisotropic and long-range. This could advance the current understanding of these highly interacting systems, while providing vital experimental data that can help verify theoretical predictions.

more information:
Boson stimulation of atomic light scattering in a very cold gas. nature physics(2022). DOI: 10.1038/s41567-022-01846-y.

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