Nat. Phys. observing chemical reactions in quantum systems
In recent years, physicists have been trying to achieve control over chemical reactions in the quantum simplex system, where the De Broglie wavelength of the particles is comparable to the spacing between the particles. Theoretical predictions suggest that many-body reactions between bosonic reactants will be characterized by quantum coherence and bosonic enhancement in this system, yet this has been difficult to verify experimentally.
Researchers at the University of Chicago recently set out to observe these elusive many-body chemical reactions in the quantum simplex system. Their paper, published in Nature Physics, presents observations of coherent, collective reactions between bosonic condensed atoms and molecules.
"Many-body chemical reactions in a quantum degenerate gas."
Quantum control of molecular reactions is a rapidly advancing area of research in atomic and molecular physics.
Applications of cold molecules to precision metrology, quantum information and quantum control of chemical reactions are envisioned. Of all the goals, quantum superchemistry is an important scientific one: more than 20 years ago, researchers predicted that chemical reactions could be collectively enhanced by quantum mechanics when reactants and products were prepared in a single quantum state.
For some time now, the enhancement of chemical reactions by quantum mechanical processes has been a much sought-after research goal. These enhanced chemical reactions are called "super reactions" and function very similarly to superconductors or lasers, but use molecules rather than electrons or photons, respectively.
The main goal of the scientists' work was to observe many-body super reactions in quantum condensed gases. To conduct the experiment, they specifically used bosonic condensed cesium atoms - a strongly electropositive alkaline element often used in the development of atomic clocks and quantum technologies.
Corresponding author Cheng Chin explains, "Cesium atoms are chemically reactive at low temperatures and can be efficiently converted into bosonic condensed molecules. We monitored the dynamics of molecule formation in atomic condensates and observed macroscopic quantum coherence between atoms and molecules."
The research team's experiments yielded a series of interesting observations. They found that the superchemical reaction in the cesium atom condensate was initially characterized by rapid molecule formation. During the transition to equilibrium, these molecules oscillate at different speeds; samples with higher atomic densities seem to oscillate faster, suggesting an enhanced bosonicity of the reaction.
"Our work demonstrates new guiding principles for chemical reactions in quantum simplex systems. In particular, we demonstrate that all atoms and molecules can react collectively as a whole. This many-body reaction promises to control the advancement and reversal of chemical reactions without dissipation and to direct the reaction pathway to the desired product."
Recent work by Chin and his colleagues has helped to deepen the current understanding of quantum many-body chemical reactions, outlining a viable pathway for controlling these reactions in a quantum-simplex state. In their paper, the researchers introduce a quantum field model that captures the key dynamics of these reactions well enough to guide future experiments in this area of research.
Images of atomic and molecular Bose-Einstein condensation. (a) shows an image of an atomic Bose-Einstein condensate of 60,000 cesium atoms at a temperature of 10 nKelvin; Fig. (b) shows a molecular Bose-Einstein condensate of 6,000 Cs_2 molecules, which were created from an atomic condensate as a result of a quantum many-body reaction.
Comparison of the rates of molecule formation in the classical and quantum condensed systems
Bose-enhanced atomic molecular reaction dynamics
"We now plan to identify new fundamental laws that govern chemical reactions in the quantum many-body system." Chin added: "For example, condensed molecules are described by a single wave function, and the phase of the wave function is key to controlling the direction of chemical reactions. In addition, we will study many-body effects in more complex polyatomic molecular reactions."
Reference links:
[1] https://phys.org/news/2023-08-many-body-chemical-reactions-quantum-degenerate.html
[2] https://www.nature.com/articles/s41567-023-02139-8
