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Atomic and molecular collisions at very low temperatures

Understanding how atoms and molecules collide and scatter at temperatures close to absolute zero is important. Such temperatures are common in the universe and finding increasing use in technology.
Atomic and molecular collisions at very low temperatures
Ultracold species are having a significant impact in high-precision measurements and metrology, the study of collective phenomena in condensed-matter systems and quantum-controlled chemical reactions as well as the development of quantum technologies.

Studying low-temperature collisions is of critical importance. Collisions are fundamental in cooling materials into the ultracold regime since various cooling techniques rely on thermalisation with colder species. Collisions often determine loss rates in traps and thus the lifetime of (ultra)cold samples.

The SUPERCOLD (Quantum scattering at ultracold temperatures: a few S-matrix columns is all we need) project has achieved significant results in several of these areas. They developed a statistical formalism for (ultracold) chemical reactions in external fields. It is based on the statistical approximation to state-to-state transition probabilities (modulus squared of S-matrix elements). A key achievement, this provides the first generally tractable, rigorous theoretical framework for computing statistical product-state distributions for ultracold reactions in fields.

Analysis shows that fields have two main effects on the products of a statistical reaction. One is by modifying the product energy levels and potentially reshaping product distributions. Another is adding or removing product states by changing the reaction exothermicity. Researchers established a re-coupling methodology for approximate hyperfine effects for ultracold scattering in external fields. The new method approximately accounts for the effects of hyperfine interactions in ultracold scattering calculations in external fields.

The project has demonstrated how hyperfine effects may be added a posteriori to hyperfine-free calculations to obtain approximate hyperfine state-to-state cross sections. The new method provides a natural explanation for the main hyperfine effects identified in the literature. This can be used independently or combined with other approximations to significantly reduce the basis sizes in ultracold scattering calculations. Depending on the system considered, it may lead to a one to four orders-of-magnitude saving in computing time, opening the door for an in depth study on the hyperfine effects in ultracold molecular collisions.

Related information


Molecular collisions, ultracold species, condensed matter, quantum, chemical reactions, transition probabilities, hyperfine
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