Observation of phase doubling and entanglement generation in coherent matter-wave reactions

Chemical reactions in a statistical ensemble are conventionally regarded as incoherent processes driven by thermodynamics. In the classical regime, reactions are expected to proceed faster at high temperatures and slow to a halt in the zero temperature limit according to Arrhenius kinetics. In the quantum degenerate regime, where bosonic atoms and molecules form coherent matter waves, reactions are instead described by nonlinear mixing of matter-wave fields, leading to Bose-enhanced reactions and coherent amplification. This leads to the following question: how does matter-wave coherence evolve during a reaction and how can it affect reaction dynamics? In the quantum regime, the matter-wave phases of the reactants and products must match as a consequence of wave mixing, analogous to the phase matching of photonic fields in nonlinear optics.

In this talk, we report the observation of phase coherent reaction dynamics of Bose-condensed atoms and molecules near a Feshbach resonance. Using matter wave diffraction with optical lattices, we verify spatial coherence of both reactants and products and observe phase doubling when atomic waves combine into molecular waves, the matter-wave analogue of second-harmonic generation. The diffraction patterns further reveal signatures of entanglement generated during the reaction. Our observations establish phase coherence and entanglement as two essential features of "quantum many-body chemistry" where macroscopic quantum fields govern the reaction dynamics.