Quantum effects in chemical reactions
New research shows that chemical reactions in an ultracold quantum gas can generate entanglement and transfer phase information from atoms to molecules The post Quantum effects in chemical reactions appeared first on Physics World .
Chemical reactions are typically seen as random, probabilistic processes involving particles colliding and rearranging themselves according to energy and probability principles. However, at extremely low temperatures, atoms and molecules can act as coherent matter waves, leading to reactions that resemble wave mixing in optics. To further explore this phenomenon, researchers from the University of Chicago conducted experiments on a gas of caesium atoms cooled to a temperature of 11 nanokelvins, forming a Bose–Einstein condensate.
By employing a Feshbach resonance—a method of manipulating ultracold atoms' interactions using a magnetic field—they initiated a chemical reaction. This resonance allows two atoms to couple strongly to a bound molecular state, converting them into weakly bound caesium diatomic molecules. Through this technique, the researchers successfully transformed an atomic Bose–Einstein condensate into a molecular Bose–Einstein condensate containing around 10,000 molecules.
Their most significant finding was the observation of phase doubling—a quantum effect akin to phase matching in second harmonic generation, where two red photons in a nonlinear medium merge to create a blue photon with double the frequency and momentum. In this instance, two atomic matter waves merge to form a molecular matter wave, whose phase is twice that of the individual atoms.
Additionally, the team demonstrated that molecules created from atoms with differing momentum states were amplified beyond classical predictions, suggesting the presence of non-separable, entangled two-atom momentum states generated during the reaction. This study exemplifies quantum many-body chemistry, where reactions are influenced by the shared quantum phase of numerous atoms and molecules.
This concept bears resemblance to how the direction of a Josephson supercurrent is determined by the phase difference across its junction. The full account of this research, titled "Observation of phase doubling and entanglement in coherent matter-wave reactions," was published by Shu Nagata et al. in Rep. Prog. Phys. 89 060501 in 2026.
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